A Bayesian approach to regional ceramic seriation and political history in the Southern Appalachian region (Northern Georgia) of the Southeastern United States

Journal of Archaeological Science 105 (2019) 1–10

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A Bayesian approach to regional ceramic seriation and political history in the Southern Appalachian region (Northern Georgia) of the Southeastern United States

T

Jacob Lulewicz Department of Anthropology, Washington University in St. Louis, McMillan Hall, 1 Brookings Dr, St. Louis, MO, 63130, USA

A R T I C LE I N FO

A B S T R A C T

Keywords: Bayesian Radiocarbon Chronology Seriation Ceramics Southeastern U.S. Mississippian

In this paper, I explore multiple methods of ceramic seriation, including correspondence analysis and frequency seriation, to revise the regional ceramic sequence for the Mississippian period of northern Georgia in the Southeastern United States, a period defined by the emergence of complex sociopolitical organization and marked socioeconomic inequality. I present a Bayesian radiocarbon framework for interpreting these seriations and situating them in absolute time. As the acquisition of new data and new analyses continuously demand reevaluations of any ceramic chronology, the analytical framework outlined here offers an avenue for future ceramic and radiocarbon datasets to be formally integrated with extant datasets to quantitatively reevaluate archaeological sequences. Because changes to materials and material attributes continue to be employed to construct culture-historical narratives and timelines across the world, especially for the purpose of highlighting and defining critical social, political, economic, and cultural transitions, the methodological approach presented here provides opportunities to formally explore, assess, and re-evaluate temporalities of cultural change.

1. Introduction Seriation is one of the few uniquely archaeological methodologies and stems from the need to effectively order artifact assemblages by changes in assemblage composition over time. It is “a descriptive technique, the purpose of which is to arrange comparable units in a single dimension (that is, along a line) such that the position of each unit reflects its similarity to other units” (Marquardt, 1978:258). While traditional methods of seriation do well to order information in a relative manner, the absolute timing and temporality of changes in the archaeological record can only be elucidated through absolute dating techniques. Indeed, the results of seriation efforts are often presented alongside radiocarbon data (e.g., Smith and Neiman, 2007). Here I contribute to these efforts by presenting a case study within which radiocarbon data and information derived from regional archaeological seriations can be formally evaluated against one another within a Bayesian interpretive framework. The results of this study provide a high-resolution, absolute chronology for regional ceramic traditions from the Southern Appalachian region of the southeastern United States (Fig. 1) and contributes to broader methodological advances in archaeological chronology building worldwide. As in many parts of the world, archaeological periodizations in northern Georgia are based on gross changes to ceramic traditions.

While serving as valuable indicators of broad temporal trends, these essentialized periods often obscure important temporal variability and mask the actual temporalities of social, political, and cultural change that they seek to inform. Indeed, legacies of archaeological work rooted in culture-historic frameworks have left us with chronologically ordered ceramic “types” whose presence or absence in a particular context are used to indicate the timing of events or cultural phenomena as they unfolded in the past. In northern Georgia in particular, ceramic chronologies are used to mark temporalities and rhythms of critical sociopolitical transitions. The period considered here (AD 600–1600), played host to numerous changes including the development of centralized polities, the institutionalization of socioeconomic inequalities, the adoption of shared religious practices, and the intensification of agricultural production. While extant chronologies neatly order archaeological periods, each characterized by particular forms of social, political, and economic structures, the revised chronology presented below, based on formal seriation techniques and Bayesian modeling of radiocarbon data, suggest a much more complex historical trajectory. 2. Northern Georgia political histories The current understanding of the fluorescence of sociopolitical complexity that persisted across northern Georgia, and the Southern

E-mail address: [email protected]. https://doi.org/10.1016/j.jas.2019.02.005 Received 9 September 2018; Received in revised form 15 January 2019; Accepted 23 February 2019 0305-4403/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. Map of the study area showing the location of archaeological sites yielding ceramic and radiocarbon data used in this study. Sites mentioned in text are labeled.

abandonment as a critical mechanism of social and cultural change at Etowah and within the Etowah River valley. Following this abandonment episode, the Early Wilbanks phase (AD 1250–1325) represents the apex of Etowah's Mississippian cultural expression. During this phase, King (2003) argues that, following the reoccupation of the community, strategies of social and political organization shifted from corporate in orientation to a network-based orientation within which social inequalities and political hierarchies were made explicit through the control of widely shared ideologies and elaborate religious knowledge (sensu Blanton et al., 1996). It is during this phase that the bulk of mound construction was completed, largescale population aggregation at Etowah occurred, construction began on the ditch and palisade complex, and the extent of Etowah's influence throughout the region was at its height. The Late Wilbanks phase (AD 1325–1375) generally represents the continuation of developments that characterized the Early Wilbanks phase. At the end of the Late Wilbanks phase however, at approximately AD 1375 (per the extant chronology), Etowah underwent a rapid and violent abandonment (King, 2003:78). The analyses and results presented here contribute to refining this political chronology through the integration of formal seriation methods to determine an independent timeline of changes to the composition of ceramic characteristics over time and throughout the study area. While the previous research has been based on the use of typologies and a strong commitment to culture-historic interpretive frameworks, the current study moves beyond the use of simple

Appalachian region more broadly, between ca. AD 1000 and 1400, is derived primarily from a subjective articulation of ceramic and radiocarbon data (Hally and Langford, 1988; Hally and Rudolph, 1986; King, 2001; 2003). Admittedly, similar to the study presented here, these extant interpretations are based almost solely on investigations of sites within the Etowah River valley and, to a lesser extent, those in the Carter's Dam area north of the Etowah River valley. The current chronology for this period is divided into a series of phases including the Woodstock (AD 800–1000), Etowah (AD 1000–1200), Wilbanks (AD 1250–1375), and Lamar (AD 1425–1600) phases. King (2003) argues that the Early Etowah phase (AD 1000–1100) represents the first occupation of the Etowah site, the largest, most profound manifestation of Mississippian cultural, sociopolitical, and religious practices in the region. While the extent of occupation at this time was modest, King (2001, 2003) argues, based on evidence for feasting and communal activities possibly related to the first stages of mound construction, that new social institutions began to emerge that were corporate in orientation, emphasizing cooperation and group solidarity (sensu Blanton et al., 1996). The Late Etowah phase (AD 1100–1200) is argued to have been a continuation of the developments witnessed during the Early Etowah phase. From AD 1200–1250, it is argued, using ceramic evidence (Rudolph and Hally, 1985; Stephenson et al., 1996) that the Etowah River valley was abandoned (Cobb and King, 2005; King, 2003, 2001). Based on this argument, Cobb and King (2005) have argued for cycles of 2

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Fig. 2. Diagram illustrating seriation procedures used to seriate ceramic assemblages from archaeological sites across northern Georgia.

within an assemblage to derive an order or sequence among many assemblages (Dunnell, 1970:121–125; Lyman et al. 1997:57)” (Smith and Neiman, 2007:48). Working from a frequency table where assemblages are represented as rows and artifact types are represented as columns, frequency seriation “attempts to fit within-assemblage (row) percentages to a model that specifies how within-type (column) fluctuations should behave over time” (Smith and Neiman, 2007:49). The model for the standard or expected distribution or frequency of artifact types over time is the commonly referred to “battleship curve” which exhibits monotonic increase, a climax, and a monotonic decrease (Smith and Neiman, 2007:49). As attributes or artifact types are assumed to increase in abundance, peak, and then decline through time, the measure of success for a frequency seriation is its wellness of fit to a battleship curve (Peeples and Schachner, 2012). In instances where stratigraphic information is available, the method of frequency seriation is straightforward, as assemblages are ordered based on their relative stratigraphic positions. In other cases, where one wishes to seriate assemblages across functionally unrelated contexts (e.g., regional material culture seriations), the process of frequency seriation is much less exact. In such cases, the rows of a frequency seriation (individual archaeological contexts or assemblages) will be ordered subjectively to create a series of battleship curves across each of the material classes (columns) with the assumption that a seriation producing a sequence of battleship curves will reveal the correct temporal order of the assemblages in question. Fortunately, there are statistical methods that archaeologists might use to more objectively evaluate similarities between assemblages, order archaeological contexts, and derive temporal relationships. One of these methods is correspondence analysis.

categorization of ceramic types and does not take as its goal the simple refinement of the boundaries of essentialized culture-historic phases. Additionally, in the sections that follow, I present a mode of formally integrating ceramic seriation data with radiocarbon datasets in lieu of a more subjective “eyeball” test as has been the tradition in the past. It is important to note that while the results, and interpretations, presented here do indeed provide a refined chronological framework, they first a foremost represent a starting point from which future studies should, and will, elaborate upon. 3. Methods A combination of traditional frequency seriation and correspondence analysis is used to seriate ceramic assemblages from across northern Georgia. The benefits of combining the two procedures for ordering archaeological assemblages has been recognized and highlighted by others working with ceramic data (e.g., Peeples and Schachner, 2012; Smith and Neiman, 2007). The procedures outlined below are presented in a simplified schematic in Fig. 2. I use correspondence analysis, a statistical mode of assessing and representing variability among assemblages, to assign scores to assemblages that can then be used to order them along a gradient representing time. I then use traditional frequency seriation to verify that assemblages were successfully ordered by time as evidenced by the presence of “battleship” curves of ceramic frequencies. The theoretical justification for the use of these methods is described in more detail below but outlined more substantially by Peeples and Schachner (2012) and Smith and Neiman (2007). 3.1. Frequency seriation

3.2. Correspondence analysis The most common method of seriation is frequency seriation. Frequency seriation “uses the relative frequencies of artifact types

Correspondence analysis (CA) is “a statistical technique for 3

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here (and in other recent applications of Bayesian modeling to issues of seriation in the southeastern United States (e.g., Ritchison, 2018; Wilson et al., 2018)), the assumptions employed may serve as a working hypothesis on which the analysis is based (Bronk Ramsey, 2009a:348). Lulewicz (2018a) recently evaluated the assumptions built into the extant culture-historic framework for northwestern Georgia by iteratively incorporating a number of alternative assumptions into the Bayesian interpretation of a legacy radiocarbon dataset. Building on this recent work, I combine a suite of 28 new radiocarbon dates with 68 extant dates (Supplemental Table) and employ an attribute-based seriation as a working hypothesis about the ordering of ceramic assemblages across northern Georgia. Interpreting seriation results and radiocarbon data within a Bayesian framework, I provide precise temporal ranges for ceramic assemblages and a more accurate estimation of the timeframe for the regional ceramic sequence, thus yielding implications for interpreting precise temporalities of sociopolitical phenomena.

displaying the relationships among the rows and columns of a two-way frequency table of non-negative numbers in two dimensional space" (Peeples and Schachner, 2012:2820; for detailed overviews see Greenacre, 1984, 2007; Greenacre and Hastie, 1987). In brief, CA “operates through the decomposition of the X2 statistic for a contingency table to produce a set of orthogonal axes which account for the total variation in a frequency table” (Peeples and Schachner, 2012:2820). As an ordination technique, CA allows for the visualization, using a limited number of dimensions, of the distances between a set of assemblages whose complete description requires many more dimensions (Smith and Neiman, 2007:55) and thus is useful for defining and ordering observations along a gradient of variation (Peeples and Schachner, 2012:2820). CA relies on the assumption that the frequency of occurrence of material types in assemblages ordered across a temporal gradient will follow a unimodal distribution when plotted against the gradient itself. That is, material types will be most frequent or most abundant at some point along the gradient (in time) and will decline in abundance as gradient values depart from the optimum point (Smith and Neiman, 2007:57). As such, CA provides a method of formally assigning numerical, successive scores to ceramic assemblages that can be used to place them in a sequence which can inform, and be evaluated by, traditional frequency seriation. Importantly, CA works best when there is a single strong vector of variation across assemblages. While this may be time, it is important to note that in some cases such differences unrelated to time, as demographic scale or geography, may be observed as a vector of variation. This means that CA is most useful as a mode of seriation when there is some other independent means of assessing temporal ordering, accomplished here using both frequency seriation and Bayesian modeling of associated radiocarbon dates. In situations where there are multiple strong dimensions of variation, CA may not produce a reliable ordering with reference to only one dimension of variation.

4. Materials and procedures 4.1. Ceramic data The seriations presented here were produced using published ceramic assemblages, the sources for which are provided in Supplemental Table 2. For this study, assemblages are defined as collections of ceramic materials recovered from discrete archaeological contexts. In this case, these contexts include house floors, mound construction stages, intact midden layers, pit features, and discrete strata encountered and recorded through unit excavations. By using discrete, sub-site assemblages for this analysis, assemblages from different components at the same site are treated independently within the seriation (Fig. 2). In total, 124 assemblages from 25 sites totaling 87,704 sherds were seriated. These assemblages, including proveniences, ceramic counts, and results derived from the correspondence analyses described below are presented in Supplemental Table 2. To mitigate inter-researcher biases concerning the assignment of sherds to a particular type, named ceramic types were not used to organize the seriation. Established types were aggregated by common surface treatment (e.g., plain, incised, complicated stamped). What is clear from the extant sequence is that particular styles of complicated stamping are undoubtedly sensitive to time. For this reason, the general complicated stamped category was divided into particular stamping traditions which are based on line thicknesses, quality of execution, and depicted motifs. Besides these named stamping traditions, no other type classifications were used in lieu of generic surface treatment classifications.

3.3. Bayesian chronological modeling Bayesian statistics allow us to “analyze new data we have collected about a problem in the context of our existing experiences and knowledge about that problem” (Bayliss, 2007:75). By doing so, we can “arrive at a new understanding of the problem which incorporates existing understandings about the problem and our new data” (Bayliss, 2007:75). To use the associated terminology, new data, or observations, can be referred to as ‘likelihoods.’ In this case, radiocarbon ages represent likelihoods. Existing experiences and knowledge are referred to as “prior beliefs' or a priori information. The prior beliefs employed here is the order of ceramic assemblages from across northern Georgia as determined through correspondence analyses and frequency seriation. The resulting understandings we achieve from articulating our prior beliefs (seriations) with our likelihoods (radiocarbon dates) are understood to be ‘posterior beliefs’ (modeled absolute date ranges for sections of our seriation). More detailed and extensive overviews of Bayesian methods for the analysis of radiocarbon data can be found elsewhere (e.g., Bayliss, 2015; 2007; Bayliss et al., 2007a; Bronk Ramsey, 2009a; Buck et al., 1996; Whittle et al., 2011). Arguably the strongest prior information we have as archaeologists are the stratigraphic, depositional environments from which radiocarbon data are recovered (e.g. Aldana, 2016; Bachand, 2008; Bayliss et al., 2007b; Bronk Ramsey, 2000; 2009a; Kennett et al., 2014; Krus, 2016; Monaghan et al., 2013; Overholtzer, 2015; Pluckhahn et al., 2015; Schilling, 2013; Thompson et al., 2016). More general prior information including culture-historic frameworks, ceramic sequences, settlement patterns, and documentary evidence can also be employed as prior information (e.g. Alberti, 2013; Boaretto et al. 2005; Buck et al., 1996; Greco and Otero, 2015; Greco and Palamarczuk 2014; Manning et al., 2006; Mazar and Bronk Ramsey, 2008; Needham et al., 1998; Raczky and Siklósi, 2013; Regev et al., 2012; Turck and Thompson, 2016). When using more generalized prior information, as is the case

4.2. Radiocarbon data and model parameters Ninety-six radiocarbon determinations associated with ceramic assemblages used in the seriation were evaluated within a Bayesian interpretive framework to situate the ceramic seriations in absolute time. The a priori information used to build the Bayesian interpretive framework is derived directly from the seriation itself. That is, the order of assemblages in the seriation, as determined through a combination of correspondence analyses and frequency seriation described above, provided information that could be used to model the radiocarbon data and determine an absolute timeline for the northern Georgia ceramic seriation. All models were built and run in OxCal v.4.3 (Bronk Ramsey, 2017; 2009a) using the IntCal13 calibration curve (Reimer et al., 2013). A more thorough discussion of the mathematical expressions underlying each of the parameters discussed below is presented by Bronk Ramsey (2009a). Complete definitions, procedures, and discussions of Bayesian chronological modeling concepts and parameters has been presented in detail elsewhere (see Bayliss, 2007; Bayliss et al., 2007a; Bronk Ramsey, 2009a; Bronk Ramsey, 2009b; Lulewicz, 2018a, 2018b). 4

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typical of CA plots in which the first two dimensions are quadratically related to one another. This is often taken as an indicator that the seriation has worked and that the first two dimensions together capture a single dimension of variation. In this case, I have interpreted the second dimension as most strongly corresponding to temporal variation, which is supported by both the frequency seriation and Bayesian modeling efforts described below. The first dimension, in contrast, does not seem to present as strong a correlation with time as the second dimension. There is a very broad, rough ordering along dimension one whereby later assemblages/traditions are located on the left-hand side of the plot and the very earliest assemblages/traditions located on the right-hand side. While I cannot at present say for sure what sorts of variation (e.g., social, temporal) are being captured along the first dimension, it would seem to be a combination of both time and social factors. Given the interpretations below, there seems to be an increase in assemblage variability at roughly AD 1000 (the Etowah phase, colored green in the graphs), with more overall surface treatments accounted for in any given assemblage. This could potentially be the result of processes related to regional population aggregation as well as the opening up of regional and extra-regional networks of interaction that have long been used to characterize the post-AD 1000 landscape. In any case, using the dimension two scores from the correspondence analysis a frequency seriation was conducted. The complete, unappended results can be found in Lulewicz (2018b:433). An appended version of this seriation is presented in Fig. 4 that includes only types that make up at least 5% of the total ceramic sample used in the study. Fig. 4 does not present each individual assemblage as a row. Rather, adjacent assemblages or rows (every successive group of ten assemblages) were aggregated to distill noise and make the plot easily interpretable. The clear battleship curves indicate successful seriation along a given gradient (presumably time). What this frequency seriation clearly shows are substantial overlaps between ceramic styles through time, indicating the complexity of stylistic change in the context of shifting patterns of social, political, and economic interactions. In identifying significant, admittedly subjective, breaks in the seriation graph, four temporal subdivisions are deduced (Fig. 5). While these subdivisions represent seemingly sequential partitions in the directional seriation presented here, these subdivisions actually exhibit varying degrees of overlap in terms of their absolute temporal ranges as determined through radiocarbon data and Bayesian modeling.

The complete OxCal code for the primary northern Georgia model is provided as Supplemental Material. One of the weaknesses of traditional seriation is that it imposes a strict order on archaeological datasets. In this case, for instance, individual assemblages of ceramics must be placed in a sequence without any formal consideration of contemporaneity of assemblages. As Steponaitis (1983:89–90) points out, a formal seriation will get you in the neighborhood, but often cannot provide the exact address. That is, while we can expect assemblages to be ordered generally by time, individual locations of assemblages within the seriation cannot be taken as definitive (unless working with stratified deposits). With this in mind, the frequency seriation based on correspondence analysis was divided into a number of sub-divisions on the basis of major breaks in the battleship curves of particular ceramic attributes. Each of these subdivisions was treated as a phase for the purposes of Bayesian modeling. That is, all radiocarbon data associated with assemblages belonging to a single subdivision were modeled as a single phase that represents the general composition of ceramic attributes across a particular span of time. Once grouped into phases based on breaks in the seriation, the temporal spans for phases were modeled using sigma boundaries. Whereas the use of the boundary command assumes a uniform distribution of observations within a phase, ‘sigma boundaries’ are used to define normally distributed events (Bronk Ramsey, 2009a). Sigma boundaries issue the parameters that there are no definite start or end events (Bronk Ramsey, 2009a). Thus, sigma boundaries are appropriate for evaluating the temporal ranges for seriation data, which also assumes a normal distribution of ceramic types through time. Additionally, sigma boundaries do not impose hard starts and ends to distributions but rather they account for the waxing and waning of distributions of events. In this way, boundaries of different phases, especially when modeled as overlapping phases that do not impose a hard order on the subdivisions, are free to overlap with preceding and succeeding phases or events. Phases were treated as overlapping as opposed to sequential or contiguous because these are the kinds of temporal relationships that the models presented below attempt to address. An overlapping model does not impose a strict order. A sequential model would dictate a particular order while a contiguous model would require not only a sequential order but also direct temporal adjacency of phases. The subdivisions of the seriations described below are centered on peak abundances of particular types and, for purposes of comparison, can be made equivalent to extant archaeological periodizations (Late Woodland, Etowah, Wilbanks, Lamar). As such, increases in particular ceramic types characterize the beginnings of the subdivisions while the ends of the subdivisions are characterized by decreases in particular types. Given the nature of these battleship curves, especially the overlap of these curves, it would be a false assumption to impose definite starts and ends on each temporal subdivision as the curves associated with the frequency of ceramic types grade into one another over time. In addition to these model parameters, an outlier model was also implemented to account for the uncertainties associated with radiocarbon data derived from unidentified charcoal. Specific parameters for the charcoal outlier model follows Bronk Ramsey (2009b) and Krus, (2016).

5.2. Bayesian modeling Fig. 6 depicts the modeled start and end boundaries for each of the four subdivisions identified in the frequency seriation. Full plots of all modeled radiocarbon determinations can be found in Lulewicz (2018b:467). Table 1 provides the modeled calendar dates for each of these subdivisions. These temporal sequences are presented schematically in Fig. 7 where they are compared to extant calendar date estimations for the northern Georgia ceramic sequence. The model shows good overall agreement. Model agreement is presented as an index to assess how well all measurements agree together within the specified parameters. An acceptable model should display an Amodel value of no less than 60% (Bronk Ramsey, 2009a). The model for northern Georgia has an Amodel of 85.2%. Of the 13 alternative models described in Lulewicz (2018b) (including both sequential and contiguous phase models), all exhibit Amodel values that exceed 60%. None of the alternative models deviate significantly from the results derived from the primary model presented here. The Bayesian chronology begins to deviate significantly from the extant chronology during the Late Woodland phase, lasting at least 100 years beyond AD 1000 and placing the beginning of the Etowah phase approximately 100–150 years later than expected compared to the AD 1000 date proposed by the extant chronology. While the extant framework outlines the Etowah phase, and the use of Etowah ceramics, as lasting for two-hundred years, between AD 1000 and 1200, the

5. Results 5.1. Regional seriation The results of the correspondence analysis are depicted in Fig. 3. Time is represented along dimension two from the earliest assemblages and types at the bottom towards the latest assemblages and types at the top. It is important to remember that the results of the CA are the product of frequencies of surface treatments/decorations as they are found alongside the frequencies of many other types of surface treatments. The plot in Fig. 3 captures the “horseshoe shaped” curve that is 5

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Fig. 3. Results of the correspondence analysis depicting both individual assemblages (colored dots) and particular surface treatments (red triangles). Time is represented along Dimension 2. Colors are derived from frequency seriation subdivisions and correspond with the colors represented in Figs. 5 and 7. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

ceramics, starts sometime ca. cal. AD 1400, generally supporting the extant placement of Lamar traditions. The most significant aspect of the new Bayesian chronology is the substantial temporal overlap of the phases characterized by Etowah and Wilbanks assemblages. A review of the seriation graph shows that Etowah and Wilbanks complicated stamping undoubtedly grade into one another. This corresponds with King’s (2001) observation that Etowah ceramics are found in all Wilbanks contexts at the Etowah site. While King (2001) explained this pattern as the result of unintentional mixing, the Bayesian model

Bayesian model estimates a span of 260-420 (at 68% confidence) years, with an end date sometime ca. cal. AD 1270-1310 (68% confidence). The results of the Bayesian model suggest that the use of Wilbanks ceramics overlapped significantly with Etowah phase assemblages. The modeled start date for Wilbanks generally confirms the placement of Wilbanks ceramics in the extant chronology at ca. AD 1250. The modeled end date for Wilbanks varies slightly with the extant chronology, suggesting an earlier termination of Wilbanks ceramics, ca. cal. AD 1350. The timeline for the Lamar phase, characterized primarily by Lamar type

Fig. 4. Appended frequency seriation graph. Each row is an aggregate of ten adjacent ceramic assemblages ordered through correspondence analysis. Only surface treatments (columns) making up at least 5% of the total northern Georgia ceramic sample are depicted in the graph. 6

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Fig. 5. Appended frequency seriation graph showing four subdivision based on breaks in battleship curves. These subdivisions serve as the basis for the phases built into the Bayesian models. They are roughly analogous to extant periodizations: Late Woodland (blue), Etowah (orange), Wilbanks (green), and Lamar (yellow). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

presented here suggests some level of contemporaneity between the two traditions across the region.

Table 1 Modeled start and end boundaries and spans for each of the four seriation subdivisions depicted in Fig. 5, presented at both the 68% (top table) and 95% (bottom table) confidence intervals.

6. Discussion The seriations presented here provide an alternative perspective to extant ceramic chronologies that have traditionally employed essentialized ceramic types to neatly order sociopolitical chronologies. By illustrating the inherent overlaps between different ceramic attributes through time, particularly surface decorations, the seriations used to inform the Bayesian models constructed here have produced absolute temporal spans that in some cases lend support to extant chronologies and in other instances deviate wildly from extant perspectives. The complexity of these seriations, combined with the very nature of Bayesian chronological modeling, whereby single-year start and end dates are deemed inappropriate interpretations, provide a number of new insights into the ceramic chronologies of Southern Appalachia and raise a number of important questions concerning the timing and tempo of sociopolitical transitions across the region. The most significant limitation of this study for unraveling the political histories of northern Georgia is that the chronology presented here represents first and foremost a timeline for changing ceramic frequencies and distribution across the region and throughout time. The chronologies themselves are not built from settlement features or even necessarily from stratigraphically defined contexts. Instead, what is offered is a more precise chronology for shifting compositions of ceramic assemblages through time. Following archaeological tradition,

Seriation Subdivision

Modeled Start Boundary (cal. A.D.)

Modeled End Boundary (cal. A.D.)

Modeled Span (years)

Late Woodland Etowah Wilbanks Lamar

815–910 1135–1175 1235–1295 1345–1450

1080–1165 1275–1310 1325–1380 1575–1695

430–570 260–420 85–215 305–440

Seriation Subdivision

Modeled Start Boundary (cal. A.D.)

Modeled End Boundary (cal. A.D.)

Modeled Span (years)

Late Woodland Etowah Wilbanks Lamar

760–945 1115–1190 1190–1310 1255–1495

1045–1220 1260–1330 1315–1420 1530–1790

350–640 195–450 50–285 240–575

especially for the southeastern United States, the ceramic chronology derived here is used to lend insight on the shifting political landscape of northern Georgia. As particular ceramic assemblages are indeed associated with settlement features (e.g., can be used to determine temporal range of occupations), the chronology presented here can be used to offer a series of hypotheses concerning sociopolitical development. The following interpretations/hypotheses indeed represent a starting point

Fig. 6. Modeled start and end boundaries for each of the four seriation subdivisions depicted in Fig. 5. 7

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and 1175 with the ending of the use of Late Woodland ceramics modeled to cal AD 1080-1165 and the beginning of the use of Etowah ceramics modeled to cal AD 1135-1175. The overlap between the two types of complicated stamping techniques and the later transition between the two may indicate that when the large politico-ritual capital of Etowah was founded, a concomitant reorganization of society across the landscape may not have been as pronounced as previously hypothesized. In other words, while Etowah and a number of other small mound and village complexes across the region were facilitating communal gatherings or other corporate events associated with the use of Etowah stamped ceramics (sensu Blanton et al., 1996), many communities and populations may have remained unengaged in such activities, continuing to produce Late Woodland style ceramics. Given the expanded potential span for the maximal use of Etowah ceramics, between 260-420 years as opposed to 200 years, two sociopolitical scenarios for Etowah and the region might be proposed. The first scenario generally matches the extant narrative (e.g., King, 2003) whereby Etowah ceramics are produced as the sole ceramic tradition across the region and at the Etowah site until at least cal AD 1275 but as late as cal AD 1310. During this time, corporate political strategies were employed as evidenced by mass feasting events and the initial stages of cooperative labor projects (King, 2003). Centralized political authority had not been implemented, major work on mound construction projects had not begun to be undertaken, and Mississippian ritual paraphernalia had not yet been incorporated intensively into the sociopolitical realm. After the production of Etowah ceramics ceased, Wilbanks ceramics began to be produced, but not before cal AD 1295, at least 45 years later than proposed by the extant chronology. In this extant scenario, Wilbanks ceramics are associated with the shift from corporate sociopolitical strategies towards network-based strategies (sensu Blanton et al., 1996) as evidenced by the centralization of political authority, the adoption of a shared Mississippian symbolic corpus, and an increase in socioeconomic inequality. While the extant chronology places the Wilbanks phase between AD 1250 and 1375, the model presented here suggests that while the use of Wilbanks ceramic likely did start around this time, ca. cal AD 1235-1295, their use may have ceased as early as cal AD 1325, but possibly as late as cal AD 1380, similar to the extant narrative. The Etowah and Wilbanks phases in the extant chronology are roughly the same length, at 200 and 175 years respectively. If the first scenario outlined here is accepted, the Etowah phase could range from 260-420 years while the range for Wilbanks likely spanned between only 85–215 years, indicating that the more corporately oriented political strategies lasted much longer than strategies that employed more network-based approaches to political consolidation. In an alternative scenario, the Etowah and Wilbanks subdivisions of the seriation overlap significantly, indicating the likely concurrent production of Etowah and Wilbanks ceramics. This is in contrast to the extant narrative which cleanly orders the Etowah and Wilbanks phases and allows no overlap between the boundaries of the two phases or the production of each phase's eponymous ceramics. The distinction between the two phases in the extant narrative, and the material disjuncture between the two ceramic traditions, has been explained as the result of cycles of abandonment and reoccupation (Cobb and King, 2005). The models presented here however indicate no period of abandonment across northern Georgia or the Etowah River valley. Even if we accept the two extreme ends of the modeled start and end boundaries, with Etowah ending by cal AD 1275 and Wilbanks not beginning until cal AD 1295, this leaves only a 20 year gap, not even a generation, let alone the 50 year gap that has been proposed (Cobb and King, 2005; King, 2003, 2001). At the other extreme, the Etowah subdivision of the seriation may extend until cal AD 1310 while the Wilbanks subdivision may begin as early as cal AD 1235, an overlap of 75 years. One of the issues with building long-term, regional chronologies is the potentially weak handle on issues of mixing between earlier and later archaeological components. One of the benefits of the method

Fig. 7. Diagram comparing the extant ceramic chronology/culture-historic framework (thick bar at the left) to the modeled start and end boundaries for each of the four seriation subdivisions modeled here (thin bars).

for future research as well as a formal framework within which newly acquired data can be interpreted. Across northern Georgia, the timing of the early transition towards increased agricultural production and increased sedentism has traditionally been placed at roughly AD 800 (e.g. Cobb and Garrow, 1996; Little, 1999; Markin, 2015, 2007). Given the probable contemporaneity of a number of stamping traditions within the Late Woodland subdivision of the seriation (e.g., Napier, Swift Creek, Woodstock), the model presented here suggests that while these major social transitions often linked to Woodstock stamping likely still begun ca. AD 800, the social landscape within which these changes were enacted may have been socially, politically, and historically more heterogeneous than previously considered. The modeled end dates for the Late Woodland subdivision of the seriation continue to deviate from the extant chronological framework. Whereas the boundary between Late Woodland and Etowah stamped ceramics is often cited as AD 1000 (e.g. King, 2003, 2001; Markin, 2007), the boundary between the Late Woodland and Etowah sections of the seriation, each characterized by Woodstock and Etowah maximal distributions respectively, is situated somewhere between cal AD 1135 8

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archaeological record or the historical trajectories of the social, political, and cultural phenomena we seek to explain. In addition to these epistemological and methodological improvements, the model presented here now serves as a standard baseline by which new data can be formally evaluated in the context of extant data and analyses. New radiocarbon data and new ceramic data can be continually fed into the model presented here. In this way, absolute chronologies and interpretations of archaeological temporalities can be continuously refined within a standard analytical framework.

presented here however is that individual contexts/assemblages related to discrete archaeological features were seriated. As such, we can consult a higher-resolution perspective to explore some of these issues for the Etowah-Wilbanks juncture. All raw ceramic data referenced here is presented in Supplemental Table 2. Some mixing of Etowah and Wilbanks complicated stamped ceramics is apparent when looking specifically at Mound C at the Etowah site. Indeed, while pre-mound and core mound contexts yield almost exclusively Etowah stamped sherds (165 Etowah stamped/1 Wilbanks stamped and 118 Etowah stamped/5 Wilbanks stamped respectively), Wilbanks increases only steadily throughout the lifespan of the mound, increasing to its maximum proportion of stamped sherds (45%) in the final stages of mound use. Whether or not this mixing of stamping traditions is the result of contemporary practices or mixture of earlier Etowah stamped ceramics remains unclear, but data from two other sites lends more insight. The Long Swamp site (9Ck1), located northeast of Etowah, has yielded 5,820 Etowah stamped sherds and only 5 Wilbanks sherds. Despite the almost total ubiquity of Etowah stamping across the site, of the six available, calibrated radiocarbon determinations only one dates to before AD 1200, with the rest falling between ca. AD 1225 and 1340. This is strong evidence for an end date for the Etowah stamping tradition to be significantly later than previously hypothesized (AD 1200). Alternatively, at the Plant Hammond site (9Fl3), of the 261 sherds documented, all are Wilbanks. The four associated radiocarbon determinations from this site place it's occupation between ca. AD 1225–1350, in line with extant determinations for the Wilbanks phase (AD 1250–1375) although potentially earlier. Both of these essentially single-component examples may be used to lend support to the hypothesis that Etowah and Wilbanks stamped pottery may have been produced and used contemporaneously, although more work at the sitelevel will be needed to explore this interpretation in depth. In either case, little to no data can be confidently cited to support a hiatus between the use of Etowah and Wilbanks ceramics in the region as has been traditionally argued. The potential temporal overlap between Etowah and Wilbanks assemblages is significant in that it raises questions about the character and mechanisms of social changes that occurred after the turn of the first millennium AD. While the relationship between these two traditions remains ambiguous, it is clear that sociopolitical transformations, especially the development of Etowah as a major center of sociopolitical activity, were likely contextualized by either, or all, of the following: 1) the movement of new peoples into the Etowah River valley and the subsequent use of two ceramic traditions; 2) the heterogeneous, in situ development of two coeval ceramic traditions across northern Georgia; and/or 3) a change in ceramic tradition that developed so rapidly that the two cannot be temporally parsed out in the archaeological record. In this last scenario, changes to ceramic traditions would likely indicate the rapid reorganization of communities of practice and alterations to the relationships between social groups as evidenced through changes to social signaling behaviors both regionally and within communities.

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