The environmental context of a city in decline: The vegetation history of a Khmer peripheral settlement during the Angkor period

Journal of Archaeological Science: Reports 24 (2019) 152–165

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The environmental context of a city in decline: The vegetation history of a Khmer peripheral settlement during the Angkor period

T

Tegan Halla, , Dan Pennya, Rebecca Hamiltonb ⁎

a b

School of Geosciences, The University of Sydney, NSW 2006, Australia School of Culture, History and Language, The Australian National University, ACT 2006, Australia

ARTICLE INFO

ABSTRACT

Keywords: Preah Khan of Kompong Svay Palaeoecology Geoarchaeology Angkor Post-Angkor Cambodia Archaeology

During the Angkor period (9th to 15th centuries C.E.) the Khmer kingdom extended across much of mainland Southeast Asia. The primate city of Angkor was located on the floodplains to the north of the Tonle Sap and connected to a network of secondary cities across the kingdom via formal road or navigable river systems. Preah Khan of Kompong Svay was one such secondary city, and was positioned on the eastern margins of Khmer territory approximately 100 km from Angkor. Stylistic dating of Preah Khan's temple architecture revealed that the majority of building works was conducted between the 11th and 13th centuries C.E., however only minimal archaeological evidence for occupation during this period has been found. This paper presents a record of environmental change that re-evaluates the settlement history of Preah Khan, and suggests that occupation and land use change was occurring at least between the early 12th and late 14th centuries C.E. Signs of gradual land use attenuation and a reduction in water infrastructure management are evident from the late 13th century through to the late 14th century C.E., and during the mid-14th century an apparent shift in the utilisation of the city occurs. This study helps to address the relative lack of research into cities outside the Angkor region, and demonstrates the value of using palaeoecological evidence for unravelling the complexity of settlement history in Angkor-period cities, particularly through the waning phases of occupation.

1. Introduction Preah Khan of Kompong Svay was an important secondary centre situated on the eastern periphery of the Khmer kingdom during the Angkor Period (9th–15th century C.E.) (Fig. 1). The Angkor Period began with the reign of Jayavarman II (802–835 C.E.), who declared the consolidation of the Khmer kingdom under the cult of the god-king (Heine-Geldern, 1942; Filliozat, 1954; Higham, 2001). Thus began a remarkable period in Southeast Asia's history, renowned for the largescale architectural and engineering works, urban expansion and territorial dominance maintained by subsequent kings. By the 11th century C.E., the mainland was peppered with Khmer centres typified by highly customized agro-urban landscapes of religious monuments, rice fields and water infrastructure (Evans, 2016; Evans et al., 2013b). Navigable river and formal road networks connected these provincial centres, including Preah Khan of Kompong Svay (hereafter referred to as Preah Khan), to the capital of Angkor (Hendrickson, 2007). Preah Khan was remote from the fertile floodplains of the Tonle Sap lake but was strategically located on the frontier of the neighbouring Cham territory and proximal to the richest iron ore source in Cambodia

⁎

(Phnom Dek) (see Fig. 1) and the iron smelting communities and technologies of the Kuay people (Levy, 1943; Groslier, 1986; Dupaigne, 1987; Pryce et al., 2014). As such, Preah Khan was thought to be a strategic and economic centre servicing the primate city at Angkor, rather than an agrarian metropolis akin to its sister cities (Groslier, 1973; Hendrickson et al., 2013; Hendrickson and Evans, 2015). Recent airborne surveys of the city have uncovered the contours of a vast urban landscape, including dense urban grids, extensive networks of irrigation canals and other features that closely resemble the layouts of the classic Angkor-period cities (Evans, 2016). Yet there is little direct evidence of the large and permanent population that the urban fabric implies must have lived there (Hendrickson and Evans, 2015). The city was initially documented by colonial explorers in the 19th century (Moura, 1882; Tissandier, 1896; Delaporte, 1880), but detailed surveys of the temple complex were not conducted until the turn of the 20th century. Maps produced by Aymonier (1900, 1901, 1904) and Lunet de Lajonquière (1902, 1907, 1911) outline a cityscape comprising a central sanctuary and its main reservoir (Baray, see Fig. 2c) housed within a series of rectilinear enclosures, within which smaller temples (Fig. 2a), sculptures, accessory buildings and water basins were

Corresponding author at: School of Geosciences, Room 348, Madsen Building (F09), University of Sydney, NSW 2006, Australia. E-mail addresses: [email protected] (T. Hall), [email protected] (D. Penny), [email protected] (R. Hamilton).

https://doi.org/10.1016/j.jasrep.2019.01.006 Received 11 June 2018; Received in revised form 27 December 2018; Accepted 5 January 2019 2352-409X/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. Map of Cambodia showing the geographical context of Preah Khan of Kompong Svay, 100 km east of Angkor. Contours are in 20 m intervals (low/green – high/pink). Topographic and hydrology data sourced from the Japan International Cooperation Agency (JICA) (2002).

in the 14th and 15th centuries C.E. Hendrickson and Evans (2015) have more recently constrained the latest possible date of the fourth enclosure's construction to the 12th to 14th centuries C.E. Together these assessments have helped clarify the development sequence of Preah Khan's physical infrastructure and have implied a basic history of settlement, at least for the early phases of the city's tenure. There has been a renewed focus on the settlement timeline and function of Preah Khan in the past decade, and a more detailed occupation history of the city is beginning to take shape. The airborne laser scanning work of Evans (2016) may potentially document an outward expansion of urban occupation in the 12th and 13th centuries C.E., given the resemblance between the urban layout of the central sanctuary at Preah Khan and the early 12th century grids within Angkor Wat and Beng Mealea. The urban layout outside the central enclosure of Preah Khan is also analogous in form and scale to the more sprawling, less-organised cities associated with the later period of Jayavarman VII (Evans et al., 2013b, 2013a; Evans and Fletcher, 2015). Recent ground surveys of ceramic and masonry artefacts, in conjunction with multi-scalar, remotely sensed datasets, and the absolute radiocarbon dating of iron slag deposits within the city and in the surrounding landscape, suggest that use of the city may have extended well beyond the 13th–14th centuries, and possibly into the 17th century C.E. (Hendrickson et al., 2013; Hendrickson and Evans, 2015). This work has exposed the strong political function of the city and its potential importance to the Khmer elite as a symbolic expression of state power in an important, resource-rich region. Hall et al. (2016) suggest that limited but persistent domestic populations conducting relatively

also scattered (see Fig. 3). During a subsequent aerial survey, an additional 4.8 × 4.8 km enclosure was discovered (Goloubew, 1936), making Preah Khan the most extensive (at almost 23 km2) rectilinear temple complex in the Khmer kingdom. Research into the peripheral centres of the Khmer kingdom throughout the rest of the 20th century was limited, given the remoteness of these sites and a preoccupation with the archaeology of the central region of Angkor. The work of Mauger (1939) and Groslier (1979) at Preah Khan stand out as exceptions, and our current understanding of Preah Khan's settlement timeline is based on Mauger's stylistic dating of the city's temple architecture and a single dated inscription (K. 161, dated 1010 C.E. (Kern, 1880)) found at Prasat Kat Kdei. Mauger's analysis traces the city's construction over four phases, beginning in the early 11th century C.E. The first phase includes the erection of the central temple along with the first and fourth enclosures, followed by construction of the second enclosure in the early 12th century. He suggests that the third, fortified enclosure was completed toward the end of the 12th century, and that building works culminated in the completion of the baray and the temples of Preah Stung and Preah Thkol in the early 13th century C.E. Recent radiocarbon dating of sediment within the baray, however, suggests that the city's main reservoir was more likely excavated during or shortly before the mid-12th century C.E. (Hall et al., 2016), almost a century earlier than Mauger's original assessment. Jacques and Lafond (2004) have also questioned aspects of Mauger's chronology, arguing that the (unfinished) construction of the outer defensive enclosure did not begin until the period of increased military pressure from the western kingdom of Ayutthaya 153

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Fig. 2. Remains of architectural features throughout Preah Khan. a. Examples of remnant Prasat (temple) architecture within the temple complex. b. The eastern gopura or entrance gates to the city. c. The northeastern, permanently wet section of the baray, looking from the west, showing colonizing vegetation of Cyperaceae, Nelumbo nucifera and Nymphoides sp. All photos courtesy of L. Radvan.

2. Environment of the study area

low-intensity land uses, at least between the mid-12th and mid-14th centuries C.E., accompanied the city's tenure. These same authors document a brief period through the remainder of the 14th century when either an increased influx of Khmer or, more likely, minority populations from the surrounding landscape instigated an increased period of biomass burning in the local catchment and began practicing iron smelting within the central sanctuary itself (Hendrickson et al., 2013), before largely abandoning the temple complex and its surrounds by the turn of the 15th century (Hall et al., 2016). This work was based on sedimentary, geochemical and charcoal proxies for occupation and land use, but lacked the more comprehensive view of urban ecology and land-use that is required to ascertain the intensity and continuity of occupation, the timing of any reductions in population and land-use, or when the city may have finally been abandoned. This paper will therefore test existing narratives about the occupation and utilisation of Preah Khan during the Angkor period using a palaeoecological analysis of sediment archives from within the city. The value in this approach has been proven for several other cities in the Khmer kingdom, where palaeoecological reconstructions have resulted in significant reappraisals of long-held theories concerning occupation sequences and the timing and extent of population declines (see Penny et al., 2006; Penny et al., 2007; Hall et al., 2018). The physical scale of Preah Khan and its underlying urban fabric (Evans, 2016), as well as its industrial and economic significance (Hendrickson et al., 2013), implies significant and ongoing investment by the Khmer elite over time, reflecting its importance within the kingdom. It is not evident whether the city was managed with direct influence from Angkor, or semi-autonomously, but through a better understanding of the city's function and occupation history, its relationship with Angkor and its place within the broader kingdom can be better understood.

Preah Khan was built on the peneplain landscape of central Cambodia, which comprises Quaternary-aged alluvial deposits intermixed with extensive Triassic and Jurassic-Cretaceous aged basement rock (Pryce et al., 2014). Soil types vary between acid lithosols, grey hydromorphics and plinthite podzols (Crocker, 1962). The topography varies little across the plain, however geographic relief can reach approximately 500 m due to the sandstone outcrops that border the catchment (Contri, 1972). The climate of the region is profoundly seasonal, with approximately 90% of annual precipitation (1400–2000 mm) falling within the summer monsoonal period between May and October (Wang and Ho, 2002). In such a climate, dry dipterocarp forest dominates the landscape – an important deciduous forest component of the Tropical and Sub-tropical Dry Broadleaf Forest Biome (Olson et al., 2001). In Southeast Asia, this forest type is often dominated by genera of the Dipterocarpaceae family (particularly Dipterocarpus, Hopea, Shorea), but also commonly comprises Adina spp., Terminalia spp., Schleichera oleosa, Dillenia spp., Xylia xylocarpa, Irvingia malayana, Lagerstroemia spp., and Sindora siamensis. Depending on the canopy structure and the prevalence of Dipterocarpaceae species, this forest type is often differentiated further into deciduous dipterocarp forest (DDF) and mixed deciduous forest (MDF) types (Bunyavejchewin et al., 2011). In patches within and surrounding the city where soils contain higher moisture retention capacity, pockets of semi-evergreen, broadleaf dry forest (SEDF) also persist in the landscape. SEDF often contains additional species such as Elaeocarpus spp., Tetrameles nudiflora, Trema tomentosa and Mangifera indica (Bunyavejchewin et al., 2011). 154

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Fig. 3. Archaeological map of the Preah Khan complex, identifying the main religious features, modified from Hendrickson and Evans (2015). Archaeological map is superimposed over a land cover and land use map of the region, with data sourced from JICA (2002).

3. Materials and methods

with wide tails during the error modelling process (Christen and Perez, 2009). A comparison of the two calibrated data sets is provided in Table 1. On average the offset between the two age models is −0.2 ± 6.7 years. The weighted mean of the modelled Bacon chronology is used to place the vegetation analysis results presented here in a temporal context. The broad conclusions from Hall et al. (2016) have been adjusted to the new Bacon-modelled chronology when they are included in the discussion. The pollen and spore extraction procedure followed the standard method outlined in Faegri and Iversen (1989). One tablet of Lycopodium clavatum marker spores was added to each sample (batch #1031, concentration 20,848 ± 691.4 grains per tablet, from the Department of Quaternary Geology, Lund University, Sweden) to facilitate absolute pollen abundance and concentration calculations (following Maher Jr, 1981) in addition to relative pollen abundances. L. clavatum is not found within Cambodia and is restricted to mountainous regions in

The palaeoecological analysis of this study was performed on a sediment core (PKKS-C1) previously described in detail in Hall et al. (2016). A total of eight cores were extracted from the baray, correlated using in-field magnetic susceptibility analysis (Fig. 4), with the longest (and therefore presumably oldest) continuous record (166.5 cm) selected for further analysis. Fig. 4 includes a description of the lithology of each core, while details of the core extraction techniques, core logging protocols and dating procedure can be found within Hall et al. (2016). The original chronology for core PKKS-C1 (Hall et al., 2016) – based on AMS radiocarbon dating – was recalibrated and remodelled here using the Bacon software package (Blaaw and Christen, 2011) in R (R Development Core Team, 2013) (Fig. 5). This program incorporates or manages outlying dates and the ‘scatter’ inherent in the probability distributions of 14C measurements by applying Student's t-distribution 155

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Fig. 4. Core correlation for all cores retrieved at PKKS. Stratigraphy, magnetic susceptibility readings, and core locations are shown.

Samples (1 cm3, n = 21) were selected for pollen analysis at approximately 10 cm intervals down-core, ensuring that all lithological units were sampled where possible. The resolution was increased in core sections where significant changes in the floral assemblage were evident. Pollen classification terminology followed Punt et al. (2007) and Huang (1972). Pollen counts per sample continued until at least 100 arboreal specimens were counted. All identified taxa were split into

Southeast Asia and so is unlikely to be found in the catchment of this site (de Winter and Amoroso, 2003). Pollen and spore reference images and morphological descriptions were collected from the Australian Pollen and Spore Atlas (Australian National University, 2016), and tropical pollen collections from Barro Colorado Island (Roubik and Patino, 2003), north-eastern Cambodia (Maxwell, 1999), Taiwan (Huang, 1972) and north-eastern Thailand (Penny, 1999). 156

Journal of Archaeological Science: Reports 24 (2019) 152–165 mem.strength: 4 mem.mean: 0.7 34 5cm sections

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4000 6000 Iteration

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5 10 15 Acc. rate (yr/cm)

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0.4 0.6 Memory

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cal yr BP 600

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0.3

Log of Objective −135 −125 −115

acc.shape: 1.5 acc.mean: 2

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0

50

100

150

Depth (cm)

Fig. 5. Age-depth model, plotted in Bacon. Top left panel depicts the MCMC iterations. Prior and posterior information is included at the top centre and right, including accumulation rate (centre) and the variability in the accumulation history (right). Calibrated radiocarbon ages are included individually in pale purple. Red curve indicates the weighted mean age for each modelled depth and grey stippled lines indicates the 95% confidence intervals for the final model.

either arboreal (including woody shrubs) or herbaceous groups (including pteridophytes and aquatics). Taxa are expressed according to their relative abundance within these groups (in Figs. 6 and 7) and plotted stratigraphically using the software package C2 v1.7.6 (Juggins, 2014), or as absolute abundances in Fig. 8. See supplementary material (Fig. S1) for pollen and spore data plotted as relative abundances calculated as percentages of the total pollen/spore sum. Major zones of transition in the vegetation assemblage were identified by a stratigraphically constrained cluster analysis, performed using the statistical packages ‘rioja’ v0.9.6 (Juggins, 2012) and ‘vegan’ v2.2.1 (Oksanen et al., 2015) in R (R Development Core Team, 2013). The CONISS and Euclidean distance methods were utilised on percentage data (both arboreal and herbaceous), and the number of zones was assigned using a broken stick model.

sorted sandy mud, which become more organic toward the top of the core. For more detailed descriptions of core sedimentary data refer to Figs. 4, 8 and Hall et al. (2016). Calibrated age ranges are presented in Table 1 and the modelled chronology is presented in Fig. 5. Prior information set in Bacon included a mean accumulation rate of 2 years/cm (estimated from top and bottom calibrated radiocarbon ages), a minimum depth of 0 cm and maximum depth of 166.5 cm. Bacon excluded both Beta-282654 and Beta-282655 as outlying dates incapable of being incorporated into the model (likely due to modern carbon contamination, see Hall et al., 2016 for further discussion). The unusually high overall sedimentation rate (0.48–0.55 cm yr−1, depending on the model used) calculated from this chronology is discussed in Hall et al. (2016). 4.2. Pollen and spore records

4. Results

84 pollen and 6 spore types were identified from 21 samples between 0 and 156 cm. Where the identification of a species or genus was not conclusive, the classification was assigned either one of the following qualifiers, ‘cf.’ (for comparable form) or ‘sf.’ (for similar form). Those classifications assigned ‘cf.’ had either minor differences in pollen

4.1. Chronology and sedimentology Twelve stratigraphic units are evident in core PKKS-C1, with no apparent hiatuses. These units are broadly characterised as poorly157

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Table 1 Table of the measured conventional radiocarbon ages (in years B.P.), including errors, and calibrated age ranges (in calendar years C.E.) of radiocarbon dated samples submitted for analysis. Final two columns compare the original modelled median from Hall et al. (2016) to the updated weighted mean modelled in Bacon. Sample ID

Depth (cm)

Material dated

Radiocarbon age (14C years BP ± 1σ)

Calibrated age range (C.E.) (2σ probability) OxCal

Bacon 1735–1799 1615–1676 1503–1592 1391–1458

[18.7%] [43%] [33.2%] [95%]

1334–1391 1271–1329 1383–1420 1317–1354 1263–1417 1232–1246 1802–1952 1682–1730 1357–1380 1260–1314 1229–1251 1153–1265 1586–1618 1411–1506

[43.7%] [51.2%] [51.9%] [42.8%] [92.8%] [2.1%] [75.7%] [19.2%] [13.3%] [73.1%] [8.4%] [95%] [9.9%] [85%]

Beta-282652

10–11

Macroplant material

270 ± 40

1628–1670 [8.6%] 1456–1582 [86.8%]

Beta-282653

30–31

520 ± 40

1393–1450 [95.4%]

OZN549

31–33

Macroplant material Wood fragments

703 ± 40

OZN553

31–35

Bulk organics

593 ± 26

OZN550

35–36

Wood fragments

672 ± 69

Beta-282654

85–86

100 ± 40

OZN552

86–88

Macroplant material Bulk organics

1380–1424 1342–1346 1380–1420 1339–1345 1365–1418 1335–1347 Outlier

740 ± 29

1360–1368 [1.5%] 1268–1322 [93.9%]

OZN551 Beta-282655

130–135 140–141

Wood fragments Macroplant material

867 ± 30 450 ± 40

1162–1264 [95.4%] Outlier

morphology to the species or genus identified, or the species/genus identified represented taxa unlikely to be found in this region. Those assigned ‘sf.’ had pollen morphology in which many, but not all, of the characteristics of that genus/species was identifiable. An average of 375 total pollen and spores (ranging from 288 to 731) were counted per sample. Stratigraphically constrained cluster analysis demarcated three major sample clusters (CONISS), indicating three successive vegetation phases (see Fig. 6). Zone 1 extends from 156 to 86 cm depth. This includes a gap in the data between 152 and 132 cm where very few pollen and spores were recovered, coincident with a peak in bulk accumulation rates (at 146–138 cm). The remainder of this zone is dominated by Elaeocarpus/ Tetrameles, Macaranga/Mallotus, Ficus, and the extra-regional species Pinus and Celtis cf. in the arboreal component (Fig. 6) and grasses and sedges (Poaceae and Cyperaceae) in the herbaceous pollen sum (Fig. 7). Cyperaceae and Amarantheacae reach their highest relative abundance in the record. Several forest taxa, including Aglaia, Anacardiaceae, Cephalanthus cf., Dipterocarpus, Hopea/Shorea, Quercus cf., Lithocarpus/ Castanopsis, Urticaceae/Moraceae and Trema are at their most well-represented. Fern spores occur frequently, but their relative abundances are fairly low. A number of herbs commonly found in the forest understorey or on cleared and agricultural land, such as Asteraceae (with fenestrate/lophate pollen morphology), Brassica cf., Colocasia sf. and Justica occur frequently in this zone. Zone 2 extends from 86 to 37 cm depth and is dominated by Combretaceae/Melastomaceae, Macaranga/Mallotus, and Myrica in the arboreal assemblage. Of the extra-regional forest species, Pinus remains well represented and Betula cf. increases. Peaks in Adina/Nauclea cf., Altingia, Engelhardia and declines in Trema, Celtis cf., Elaeocarpus/ Tetremeles, Ficus, and Hopea/Shorea occur. Pandanus and Lagerstroemia are frequently represented. The relative abundance of Schleichera oleosa increases substantially toward the end of this zone (from 0 to 16.5% of the arboreal pollen sum). Poaceae progressively dominates the herbaceous pollen assemblage through this zone (i.e. increases in both relative and absolute abundances). Ferns are poorly represented, except for a small peak in Pteridium spores at the beginning of this zone (86–77 cm depth). However other aquatic taxa, such as Nymphoides and Persicaria, occur frequently throughout the zone. In particular, a distinct peak in Nelumbo nucifera occurs from 47 to 37 cm depth. A marked shift in the arboreal assemblage occurs in Zone 3 (37–0 cm depth). Taxa that had been poorly represented in zones 1 and 2, such as Eugenia and Schleichera oleosa, now dominate the arboreal

[94.9%] [0.5%] [94.4%] [1.0%] [93.3%] [2.1%]

Modelled median (OxCal)

Weighted mean (Bacon)

1452

1469

1407

1409

1399

1403

1398

1400

1394

1394

N/A

1298

1294

1294

1214 N/A

1209

pollen component. Uncaria/Wendlandia cf., Myrtaceae, and Elaeocarpus/Tetrameles are also well represented. Decreases in the relative abundance of Urticaceae/Moraceae (both di- and tri-porate types), Quercus cf., Pinus, Ficus, Celtis cf., Pandanus, Trema, Macaranga/ Mallotus, Lagerstroemia, Lithocarpus/Castanopsis, Hopea/Shorea, Altingia (presumably A. siamensis Craib.) and Euphorbiaceae occur. Of the herbaceous taxa, while Poaceae remains prevalent, Cyperaceae declines to its lowest levels in the record (in both relative and absolute abundances). Most dryland herbs diminish in abundance, except for isolated peaks in Asteraceae and Amarantheacae toward the top of the record. Ferns increase, and peaks occur in many wetland herb taxa, particularly Rotala, Persicaria and Nymphoides. 5. Discussion 5.1. Preah Khan as an Angkor-period ceremonial and agro-urban complex Varying levels of disturbance in the forest catchment and fringing swamp vegetation surrounding the baray are classified into three vegetation zones apparent in the pollen and spore record (Fig. 8). Zone 1, which extends from the construction of the baray in the mid-12th century to the late 13th century C.E., is characterised by low concentrations of local forest pollen (identified here as pollen produced from species common to lowland dry tropical forest types such as DDF, MDF and SEDF), and low abundances of herbaceous swamp vegetation (Fig. 8). The relative abundance of extra-regional forest species is high, further indicating an underrepresentation of local dryland arboreal taxa through this zone. Indicators of forest fragmentation, such as dryland herbs and the common open forest/disturbance genera Macaranga/ Mallotus (Whitmore, 2008; van Welzen et al., 2014) occur frequently through this period. From Hall et al. (2016), the mid-12th to mid-14th century C.E. is characterised by high levels of erosion (evidenced by high and variable rates of lithogenic element influx and bulk sediment accumulation into the basin) and low-intensity local fire events, which suggests disturbance and active management of the local landscape (Anderson and Wahl, 2016; Penny, 1999). Additionally, the fact that concentrations of ferns and aquatics growing within and along the littoral zone of the baray are very low (as was the influx of organic material into the reservoir; Hall et al., 2016), suggests that the city's major reservoir was being actively maintained as an open water body between the mid-12th and at least the late 13th century C.E. Alternatively, the higher lithogenic influx during this period (Hall et al., 2016) may have 158

14 C date (yr BP ± 1σ)

1450

867 ± 30

159

1200

1450

867 ± 30

1200

1250

740 ± 29 1300

1350

520 ± 40 1400 593 ± 26 672 ± 69

270 ± 40

14 C date (yr BP ± 1σ)

1250

740 ± 29 1300

1350

520 ± 40 1400 593 ± 26 672 ± 69

270 ± 40

Calibrated age (calendar yr C.E.)

Calibrated age (calendar yr C.E.)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Depth (cm)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Depth (cm)

e ea

)

he nt

e ea

)

) ae ce

e)

at

r po

Primary / secondary dry forest

Primary / secondary dry / swamp forest

0.04 .0.218 ..6.0 4 000 0 6 12 0 20

1.0 30 15 0

Swamp forest

02 .0.06 .18 .4..0 000 02 .01.0 .06 ..4.8 2 000 0 3 60

e)

Primary dry / swamp forest

20

a ce

0018 ..6.0 20

Swamp / secondary dry / extra-regional forest

5 0 3 6 0 3 6 0

ac

5 0 10

1.0 6 20 0

120

e)

Extra-regional forest

a ce

1.00 5 0.01.0

20 40 60 0 4 8 0

10

10

20

pe y .t

1

pe y .t

2

Indeterminate ecology

20 0

Zone 1

Zone 2

Zone 3

0 2 4 01.02 4 0

0.0

10 20 30 0

3

0.01.0 000 0.04 .0.2..68 0

2

3 0

5 0

10 20 30 0

0...24 1.5000

0 5 10 0

20

400

5

relative abundance of arboreal pollen counts (%)

0 5 10 0 2 4 0

0

3 0

4 0

2

000 02 .0.06 .18 .4..0

0.0

1.5

Zone 1

Zone 2

Zone 3

e) cf cf lla e) ea e) ae eae hy ) ae) ea a m ac e p e c i i ) a e ) iu a e ce ac dac ub hn ) ) ea ce ca ) yd nd lide eae if. R nd in ap ) cr la ae if. e) ae ac c e) rbia an ae .( pi nd e ) e a g e s ) f D a a ) . a e a ap ( u d g l e a c f nd c u o / D ae a ae ce e am etu di /S /S e u ce pho an ac in (Fa (J a s m ce cea e a a n c e e a m e i e u u a l m i l l P i c u a a u a a ll p c c a a um f. ac (B U ce yr fo el e re (E us ( di ce ce ar rpa hy or in ce ia .( (H cf. au ui eg c M S (M har (A ip ea rd cf na n a nda oc ca (L cus s (P /N ia ( s (M ia c n a IS l Aq ca ynia dan a d a l s a g ( a c m m r h o N u ri a a pi tu ge lti p rt in la icu ac x sia ue Po od tin re Bre an n O y h h a e y a e n l t d g i n e l A I C R R S B E C D A M P A A P A F M In Q (P

0.0 1.5 0

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) if. e) te ) ra nd ea e) o u c a ae p a a a ce c ra bi di (tri ce ae ) i ) g r ( c a a a o e e b e a o ) ) ) p d a rpa f. f. u hl e) ut ac (F ea in di di ar ph ae ) ae ae e) ) ce (R (R ae) . (C ea m es c ia oca ea sis ace ace ap un un ace f. ae roc Eu f ac to ae el rpa ) r b m ( . c S e s r c p s i e e e e f e r ( t c m a lu if n s a e c a a s h i a no te di ia ec Ru ub el m tu ba Dip f. sa tre oc ea ca oxy ter ctu Lyt e) ce ce R . ( (Dip orb sta Ar nd un llo ha ra ora ou a ( eo cf h a Te lae rtac .( m( di e/M ba nth Gut ere ia ( cea dla e l a r / f R o p n a o s s a ( s c e C M y u cea u M /M . u /E om /Za m ( us m ma a en ce or im hu rpu (Eu us/ a/ ra e sf e/ e l e rp ae (M rm le (B ia a nt S (S /Sh ea eta s he ng x na xylu nth stro (U ia/W cea cea ca cae nia rb u es arp auc spe c l a r oc a r c IS a i t a a e o r i o h a a a r r b a e a a b N p h a pe oc te us ato lor ge em ca ae tisa uge ph ic rtic hl ng ope rec om y c O l on nco om i t a c z u r n la h a ip r ry ith ep e v E a C H S A E E C M Ir Tr U U U Zi B C D D L C C L C O N (D

Primary dry forest

(caption on next page)

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Fig. 6. Relative abundances of pollen taxa, including only trees and woody shrubs. Primary forest types include those genus/species associated with the lowland dry forest types (deciduous dipterocarp forest, mixed deciduous forest and semi-evergreen, broadleaf dry forest). Extra-regional forest includes those genus/species associated with highland forest communities. Ages are presented as uncalibrated radiocarbon dates including one standard deviation error (68%), plus calibrated calendar years C.E., calculated as the weighted mean of the two standard deviation (95%) calibrated age range.

restricted the growth of macrophytes within the baray. However, there is a moderate positive relationship (r = 0.428) between mineral accumulation rate (see Hall et al., 2016) and percentage of herbaceous wetland pollen over the entire record, suggesting that high lithogenic influx is unlikely to have been the cause of low fern and aquatic vegetation growth in the baray between the mid-12th and mid-14th centuries C.E. The archaeological record for the city (see Fig. 9 and references therein) indicates that the majority of monumental construction occurred between the early 11th and the late 13th centuries C.E. Incorporating the palaeoenvironmental data presented here and in Hall et al. (2016), it appears that a degree of ongoing landscape management, potentially reflecting human activity, accompanied this building program, at least from the mid-12th century C.E. During the final phases of building construction and beyond into the mid-14th century C.E., the local and/or regional forest appears to have been sparse and fragmented, and a low-intensity burning regime was operating in the local catchment in keeping with a landscape actively managed for either agriculture (Anderson and Wahl, 2016; Penny, 1999) or other urban uses. Together, these data suggest that ongoing landscape disturbance was occurring through this period and likely represents human occupation in a growing city (see Evans, 2016). Land use during this time was likely more intensive than previously assumed (see Hall et al., 2016; Hendrickson and Evans, 2015), and the city was seemingly being maintained as a large ceremonial outpost of the Angkor-period Khmer state, and as an agricultural and economic centre in its own right.

from its margins (Fig. 8). The growth of aquatic vegetation, accompanied by the mid- to late 14th century increase in organic matter deposition within the baray reported by Hall et al. (2016), suggests a cessation in the maintenance of the reservoir as an open water body. While a reservoir colonised by aquatic vegetation could still be useful to a local population for irrigation purposes, it is unlikely that this reservoir was ever utilised significantly for agricultural production at Preah Khan, or ever integrated effectively into its hydraulic system (see Hendrickson and Evans, 2015). Given its clear integration into the city's religious infrastructure layout, however, it is reasonable to believe that the baray was maintained as an open water body for symbolic purposes throughout the city's tenure (perhaps in addition to fisheries or other aquatic resource management purposes). As such, the development of an encroaching herbaceous swamp community across the baray potentially signals a waning in the religious function of the city in the midto late 14th century C.E. The transition from Zone 1 to 2 (at 86 cm) in the pollen and spore record begins in the late 13th century – over a half century earlier than the transition from Hall et al. (2016)'s Stage 1 and 2. This is largely due to Hall et al. (2016)'s occupation stages being predominantly based on the macrocharcoal record, which shows clear and sustained peaks in the mid- to late 14th century. Incorporating the pollen evidence presented here it appears that the gradual waning of intensive land use practices had potentially begun by the late 13th century, and therefore prior to the mid- to late 14th century increase in fire activity in the local catchment. However, the peak in local fires coincides well with the peak in herbaceous swamp community growing within the baray, and therefore coincides with evidence for the cessation of maintenance of the reservoir as an open water body. As such, this shift in the burning regime may represent a reduction in active management of the landscape for urban and/or agricultural uses and the return of more natural, variable burning regimes (particularly through the dry periods of the 14th century (Buckley et al., 2010)).

5.2. Late 13th century reduction in land and religious infrastructure use at Preah Khan Zone 2, representing the late 13th century to the end of the 14th century C.E., reflects either better preservation of pollen and spores or larger pollen yield from the surrounding flora. Total dryland pollen counts are relatively high through Zone 2, compared to Zone 1 (see Fig. 8), reflecting an increase in the number of pollen grains counted in order to achieve a sufficiently large representation of arboreal taxa in the pollen results. However, differential preservation is likely only a minor influence here, given that the proportion of unidentified/damaged pollen grains ranges between 2–8% in Zone 1 and 1–5% in Zone 2. Lowland dry and semi-evergreen forest species are abundant through the late 13th to the end of the 14th century, and the abundance of both Macaranga/Mallotus and dryland herbs is the highest in the record. Other species that can be indicative of secondary forest or forest disturbance, such as Trema and Engelhardia (Maxwell, 1999; Dy Phon, 2000), are also common in this zone (see Fig. 5). The fact that local forest pollen yields are higher, and the abundance of secondary forest species has increased, may be indicative of secondary forest recovery beginning in parts of the catchment. The abundance of Schleichera oleosa, a species that regularly invades degraded landscapes (Maxwell, 1999), often in swampy soils or wet forests (Dy Phon, 2000), increases throughout Zone 2, further suggesting a gradual attenuation in land use intensity around the baray. Additionally, the degree and variability of lithogenic flux into the baray has begun to decrease by the early to mid14th century C.E. (Hall et al., 2016), suggesting some forest recovery and landscape stabilisation at this time. Toward the end of Zone 2, during the mid- to late 14th century, a herbaceous swamp community, comprising ferns and other floating aquatic vegetation, has either colonised the baray or begun encroaching

5.3. Potential shift in the function and use of Preah Khan However, several lines of archaeological evidence indicate that occupation and use of Preah Khan did not terminate here (see Fig. 8). Hendrickson et al. (2013) document a distinct period of heightened iron-smelting activity, evidenced by dated iron slag deposits, between the late 13th and late 15th centuries C.E., possibly extending into the 17th century C.E, and several deposits of post-14th century surface ceramic and glazed wares have been discovered within the enclosure limits (Hendrickson and Evans, 2015). This period was also significant for the primate city of Angkor, as the era of territorialisation and expansion instigated by the kings of Angkor had ended by the late 13th century C.E. (Lieberman, 2003; Lieberman and Buckley, 2012), and management of Angkor's large-scale water infrastructure network had also ceased (Fletcher et al., 2008). Who was responsible for this late 13th century increase in industrial activity at Preah Khan is therefore open to interpretation (see Pryce et al., 2014). The cessation in new building construction, the pollen and sedimentological evidence suggesting secondary forest recovery, and the colonisation of swamp vegetation across the baray, suggest a shift in the function of the city and its infrastructure had occurred (i.e. from religious and urban-agricultural to industrial). As political power appears to have waned in Angkor at this time, the peak in local burning identified by Hall et al. (2016) may represent industrial burning for iron production by minority, forest-based groups living in the uplands surrounding the city, who were known for their iron smelting expertise 160

14 C date (yr BP ± 1σ)

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Calibrated age (calendar yr C.E.)

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0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

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Zone 1

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Zone 3

ac e) e) te e) on ) ea in b ea la c e e) te ea m c a a m e ) c a a a cu a ) la h e l s e) l u i i e i a t e t at t ) e e e c . e e a t f in re ps la Ba ea (Ne ac hn por an ed or ore if. ac ae di e) er ea ra u e c r f y n t m a p e e i c e c n a ( r . t r s o s f s sp n d c c le a u e te o ca ia ra ra at at en te di ns e ru yg ne e . (B late Ar ha ac sp or or As rio ifol nag cife (M at a t e e u ol de un en a (C .( nt ndi f lp i lp ea e er E (fe c .( n f r t P s l ( n f I s . a t a c o o D e u h ( u s / ( e e e c e c c p c a (O n a u sf rr gu os ila yt id ia la a ia ns on ra e/ e e/ th ( A ae ea ea m ce (L ps ve ru in ul oce igia bo ar at at isi ho iu ch olet ica a as an ac rac ra ow a c e a e e e m p p l r p s c i d m c o r l l t t t i m i e r n c c w u a a o rs a te te st te as io yd d elu er ile ile ile g en co co on yp ol nk ym ot As As Ar Br C Ju Pe Pt M Tr 44U Am Po C E r H Lu N N T r T r Le R St

e) at

Wetland herbs / aquatics and ferns e) ea

Fig. 7. Relative abundances of pollen taxa, including only terrestrial and aquatic herbaceous taxa, plus those unclassified into plant type groups. Ages are presented as uncalibrated radiocarbon dates including one standard deviation error (68%), plus calibrated calendar years C.E., calculated as the weighted mean of the two standard deviation (95%) calibrated age range.

867 ± 30 1200

740 ± 29

1350

520 ± 40 1400 593 ± 26 672 ± 69

270 ± 40

Depth (cm)

Dryland herbs

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Fig. 8. Summary palaeoecological data. Several individual pollen species/genus that are particularly indicative of land use change are also displayed. Grey panels indicate successive phases of human activity and land use, calculated using a stratigraphically constrained cluster analysis on percentage pollen data. Far right column indicates the three stages of occupation determined in Hall et al. (2016), based on sedimentary, charcoal and geochemical data. Bottom: Legend for stratigraphic log (see also Fig. 4).

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162

163

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C dated wood fragment (1162–1264 [95.4%]) from the base of the baray

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High levels of sustained local fire activity4

Localised growth of mature swamp forest

Secondary forest growth

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7

6

Hendrickson et al. (2013)

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Evans (2016)

1800

High organic matter deposition in baray4

Dated iron slag deposits8

Post-14th century Thai and Chinese (blue and white) ceramics7

Herbaceous swamp community growth in or along edges of baray

Possible construction of raised east causeway joining the first and second enclosures1

Possible construction of the three Prasats Chœuteal1

Preah Thkol and Prasat Stung constructed2,6

14

Hall et al. (2016)

Hendrickson and Evans (2015)

Mauger (1939)

Jacques and Lafond (2004)

Fig. 9. Summary of archaeological and palaeoenvironmental information existing for Preah Khan, plotted against a timeline in calendar years C.E. Regions of darker colour indicate a higher probability that the activity occurred within the associated time period (where statistical probability data is available). Mauger's (1939) and Stern's (1965) building construction dates are based on stylistic dating of masonry architecture. Calibrated age range of dated wood fragment includes 2σ probability. This is the earliest calibrated (non-modelled) date collected from baray sediments. Age-depth model suggesting date of baray construction was extrapolated from dated organic material collected from sediments within the baray. Post-14th century Thai and Chinese ceramics were found in association with Post-Angkor Period metal production sites.

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High and variable sediment influx to the baray4

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Few and isolated local fire events4

Third enclosure constructed1

Preah Damrei constructed2

Alternative date for construction of Preah Khan main temple and its first enclosure1,6

Alternative time period for construction of fourth (outer), incomplete enclosure1,3

Possible outward expansion of gridded urban occupation5

Second enclosure constructed2

Sources

Imported Chinese ceramics, porcelains and Khmer glazed wares found within enclosure walls3

Age-depth model data suggests baray constructed in the early-mid-12th century4

Preah Khan main temple with the first and fourth enclosure erected2

Prasat Kat Kdei inscription (K.161) dated 1010 C.E.

Early forges and industrial workshops in operation in northern region of site. Boeng Sre (Boeng Kroam) and Prasat Beng Sre possibly constructed.1

Evidence for human activity Evidence for waning land use and/or urban infrastructure management

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(Harmand, 1876; Levy, 1943), and may have been opportunistically utilising the abandoned city. The fact that Preah Khan stands as the sole Angkor-period, statelevel city to contain iron production sites within its temple complex enclosure (discovered thus far) further supports this idea of opportunistic use by populations not associated with the Khmer state (Hendrickson et al., 2013; Pryce et al., 2014). In addition, these slag deposits appear to represent metallurgy sites that were small-scale and likely ephemeral, relative to those discovered in the broader region surrounding nearby Phnom Dek where these minority groups were dominant (see Hendrickson et al., 2013; Pryce et al., 2014). Hendrickson and Evans (2015) also argue that consent to perform such a polluting craft in close proximity to sacred temples is unlikely to have been granted during Preah Khan's religious tenure. Moreover, iron smelting is generally performed at a distance from urban areas, largely for cultural reasons (see also Hendrickson and Evans, 2015), further suggesting that smelting activity in the heart of Preah Khan's urban zone may have only occurred in the wake of depopulation. Overall, these arguments suggest that the post-14th century use of Preah Khan represents the opportunistic reclamation of urban space, possibly by small groups of Kuoy people (see Hendrickson and Evans, 2015; Hendrickson et al., 2013). How long any potential new wave of occupation at Preah Khan persisted is unclear, however. While the localised burning appears to have subsided by the 15th century, iron-smelting activity within the city and its surrounds continued into the 17th century at least (Hendrickson et al., 2013). In conjunction with the decrease in local fire activity, the transition from Zone 2 to 3 in the late 14th to early 15th century C.E. is marked by a dramatic increase in the concentration of Eugenia pollen in the baray (Fig. 8). Such a sharp and sustained increase is likely a product of highly localised production of Eugenia pollen from species growing along the margins of the baray, rather than a broader, regional forest signal. As such, we interpret this increase as the growth of mature swamp forest, of which several Eugenia spp. are important components (Theilade et al., 2011), along the margins of the baray. Mainland Southeast Asia during the 14th and 15th centuries was characterised by a highly variable climate, and persistent periods of severe drought were common (Hua et al., 2018; Buckley et al., 2010). Thus, it is probable that water levels in the baray became severely reduced through this period, and revealed large areas of marshland upon which swamp forest could develop. Remote sensing work by Hendrickson and Evans (2015) verify that water levels in the baray at Preah Khan fluctuate considerably through time.

on Angkor, at least toward the end of the Angkor period. As such, Preah Khan likely did not exist semi-autonomously, but rather as a peripheral city strongly integrated into the Angkor-period kingdom network.

5.4. Gradual abandonment of Preah Khan

Anderson, L., Wahl, D., 2016. Two Holocene paleofire records from Peten, Guatemala: implications for natural fire regime and prehispanic Maya land use. Glob. Planet. Chang. 138, 82–92. Australian National University, 2016. Australasian Pollen and Spore Atlas. Australian National University. http://apsa.anu.edu.au. Aymonier, E., 1900. Le Cambodge: I. Le Royaume Actuel. Ernest Leroux, Paris. Aymonier, E., 1901. Le Cambodge: II. Les Provinces Siamoises. Ernest Leroux, Paris. Aymonier, E., 1904. Le Cambodge: III. Le Groupe d'Angkor et l'Histoire. Ernest Leroux, Paris. Blaaw, M., Christen, J.A., 2011. Bacon manual. http://chrono.qub.ac.uk/blaauw/ manualBacon_2.2.pdf. Buckley, B.M., Anchukaitis, K.J., Penny, D., Fletcher, R., Cook, E.R., Sano, M., Nam, L.C., Wichienkeeo, A., Minh, T.T., Hong, T.M., 2010. Climate as a contributing factor in the demise of Angkor, Cambodia. Proc. Natl. Acad. Sci. 107, 6748–6752. Bunyavejchewin, S., Baker, P.J., Davis, S.J., 2011. Seasonally dry tropical forests in continental Southeast Asia: structure, composition, and dynamics. In: McShea, W.J., Davis, S.J., Bhumpakphan, N. (Eds.), The Ecology and Conservation of Seasonally Dry Forests in Asia. Smithsonian Institution Scholarly Press, Washington DC. Christen, J.A., Perez, E.S., 2009. A new robust statistical model for radiocarbon data. Radiocarbon 51, 1047–1059. Contri, J.P., 1972. Carte geologique de reconnaissance 1/200000, Tbeng-Meanchey. In: Service National des Mines de la Geologie et du Petrole, Editions du Bureau de Recherches Geologiques et Minieres. Crocker, C.D., 1962. The general map of the Kingdom of Cambodia and the exploratory survey of the soils of Cambodia. In: Atlas of Cambodia: Maps on Socio-Economic Development and Environment. Royal Cambodian Government Soil Commission/ USAID, Phnom Penh (Save Cambodia's Wildlife). de Lajonquière, L., 1902. Inventaire Descriptif des Monuments du Cambodge. Vol. I.

6. Conclusion The new palaeoecological record of Preah Khan of Kompong Svay supports the emerging description of the city as a low-density, agrourban settlement with substantial populations from at least the 12th century, and through to the 14th century C.E. The gradual attenuation of land use and infrastructure maintenance at Preah Khan occurred through the late 13th and late 14th centuries C.E., and by the mid-14th century it is possible that new populations infiltrated the city and began opportunistically utilising the space for small-scale, intermittent iron production. This apparent repurposing of Preah Khan suggests that the use and function of the city likely evolved over time in response to the shifting interests and influence of the king and his elite in the capital at Angkor. Overall, this study emphasises the critical role of palaeoecological data in reassessing the complex occupation dynamics of regional Khmer settlements and in identifying the relationships that were operating within the Angkor-period Khmer city network. Acknowledgements This work was supported by an ARC Discovery Project (DP170102574) grant and Australian Institute of Nuclear Science and Engineering Grant 11/003. Our thanks extend to the APSARA National Authority, The Cambodian Ministry of Culture, So Malay, Phon Kaseka, Chan Sovichetra, Angus Penny-Gillespie, Mitch Hendrickson and Damian Evans for their assistance with fieldwork in Cambodia. The authors would also like to thank two anonymous reviewers for their input to the final version of this manuscript. Declarations of interest None. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jasrep.2019.01.006. References

Finally, Zone 3 in the pollen record also correlates well with the results of Hall et al. (2016), who reported the highest (sustained) levels of organic carbon sequestered in the reservoir in Stage 3, from the end of the 14th century to the end of the record. Much of this organic matter influx may have been the result of the decomposition and in-wash of the herbaceous swamp taxa that had colonised the baray in the preceding half century. The geochemical and sedimentary record also reflects a reduction in landscape disturbance in the catchment, in agreement with the pollen record that suggests forest recovery, and swamp forest development around the margins of the baray, was occurring through the 14th and 15th centuries following the decrease in landscape management. The fact that gradual attenuation of land use and the shift in the function of Preah Khan began during the late 13th to late 14th century C.E. – coinciding with the waning of power in the primate city of Angkor – has two important implications. Firstly, this finding indicates that the period of transformation and eventual political abandonment of Angkor between the 13th and 15th centuries C.E. had kingdom-wide ramifications (see also Lucero et al., 2015). Secondly, the sustainability of Preah Khan as a settlement appears to have been highly dependent 164

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