Cholula An important city of pre-Columbian Mesoamerica, dating back to at least the second century BCE, with settlement as a village going back at least some thousand years earlier. seriation A method in relative dating in which artifacts of numerous sites, in the same culture, are placed in chronological order, to work out a chronology by arranging material remains of a cultural tradition in the order that produces the most consistent patterning of their cultural traits. stelae Carved stone slabs, which depict rulers along with hieroglyphic texts describing their genealogy, military victories, and other accomplishments.
Seriation is one of the fundamental techniques used in archaeology. The criticisms of the last few decades do not invalidate its usefulness, if used with due critical judgement. The basic premise is to arrange in sequence objects of material culture (anything from microliths to monumental architecture) based on degree of similarity. Variation is assumed to be the result of spatiotemporal dimensions: greater similarity implies proximity either in space or time. Seriation is most commonly used in archaeology as a means of relative dating, where the sequence is arranged from earlier to later and objects along the continuum are datable ‘relative’ to other artifacts in the class. Note that there is nothing inherent about the sequence to determine the temporal direction, i. e., which end is earliest, so this technique is generally used in conjunction with stratigraphy or other independent dating techniques.
Seriation as a concept grew out of biological classification, and its first application in archaeology is generally credited to Sir Flinders Petrie. Analyzing grave lots from discrete burial contexts, Petrie arranged the lots by similarity until he had arrived at the most internally consistent pattern. For example, some ceramic urns had pronounced handles, while others had only slight ridges where the handles had been. He assumed an evolutionary trajectory in which the handles became increasingly less pronounced through time, and used this characteristic among others to organize the assemblages.
Shortly after Petrie’s introduction of the technique, Herbert Spinden employed a variation using anthropomorphic sculptures from the Maya site of Coprin. Using body proportions from 25 stelae, including measurements of the length of the face and the chin to the top of the girdle, Spinden arranged the stelae in sequence. He was then able to recognize other patterns such as an increase in feather adornment and eye shape. The most convincing line of evidence was that hieroglyphic dates on the monuments ranged from earlier to later, in accordance with his sequence. Note that at the time the Maya hieroglyphic system was poorly understood, and Spinden’s sequence was a key to decipherment of the calendrical system.
Change through time is assumed when using seria-tion for relative dating, with the causal mechanisms relating to changing technology, availability of materials, or simply popularity. Imagine ordering an assemblage of 100 automobiles from the twentieth century based on music systems: absence, tube radios, transistorized radios, eight-track cartridges, cassettes, CDs, and MP3 players. A graph of the results, by year, would show the introduction of a new technology followed by the gradual increase in popularity, until another technology is introduced and that original type decreases in relation to the increasing popularity of the new one. This graph is typically called a ‘battleship graph’ because the diamondshaped patterns look like a bird’s eye view of a fleet of battleships.
This scheme was used archaeologically by James Ford, who created an ‘abundance matrix’ based on the percentages of different ceramic types collected from the surface of the lower Mississippi Valley. By graphically illustrating the relative frequency of each type in each collection unit on strips of paper, Ford then ordered the strips until they created the ‘best’ series of battleship curves, representing the most likely chronological ordering of the sites surveyed. An entertaining exercise in this methodology is available in Daniel and David’s An Archaeology Workbook problem on Petristan, a fictional region named in honor of Sir Flinders Petrie.
Note that these early implementations of seriation lacked rigorous means for assessing the validity of the patterns. With the rise of the New Archaeology in the early 1960s, more scientific methods were emphasized, including new dating techniques such as radiocarbon and potassium argon. While these superceded seriation to some extent, other aspects of the New Archaeology actually augmented seriation analysis. The introduction of quantitative methods, including powerful computer systems, and a scientific revolution in the philosophy behind archaeology resulted in more rigorous analysis of the data. Additionally, greater concern for anthropological models created a tighter linkage between observed patterns and inferred behavior. During the 1970s, particularly, numerous statistical methods were introduced for manipulating data, including means for testing the validity of seriated sequences (see Sampling Methods, Theory and Praxis; Statistics in Archaeology).
An example of these statistical methods for testing the results of a seriation sequence comes from a ceramic analysis of Postclassic Cholula, Mexico. Cholula was one of the largest urban and religious centers of central Mexico in the final centuries prior to the Spanish conquest. Several studies of the archaeological ceramics have been published, with Eduardo Noguera’s based on stratigraphic pits in and around the Great Pyramid, a massive mud brick structure that has undergone 2500 years of sequential use and modification resulting in a highly mixed deposit. For his evaluation of the existing ceramic sequence, McCafferty chose dispersed primary deposits from the UA-1 residential compound about 1 km from the Pyramid. Thirteen midden assemblages contained polychrome and monochrome pottery that was classified into 19 types.
The seriation analysis proceeded in steps. First, each pair of assemblages was converted into similarity coefficients using the Brainerd-Robinson Index of Agreement where the total difference between the percentages of each type is calculated, and this total is subtracted from 200% (the maximum possible level of disagreement). Thus, a high index value will show greater similarity, and a low value will represent greater dissimilarity. A. E. Gelfand recommends a method for generating a seriation, that is, both rigorous and replicable, where the Brainerd-Robinson values are systematically sorted by order of similarity and then the rankings of each row are averaged to produce the best possible seriation. The final step was to calculate the average rank order for the 13 different seriation results. The rank average is determined by dividing the rank totals by 13. These rank averages were then graphed to show not only the order of the assemblages, but also clusters based on similarity. As a result of this analysis the Cholula Postclassic ceramic sequence was significantly modified, and clustering of assemblages was used to refine the Postclassic chronology into five subphases.
One of the most eloquent demonstrations of the validity of seriation analysis derives from historical archaeology, where grave monuments encoded detailed iconographic symbolism, variations in form and material, evidence of technological change in terms of carving and transportation, and all important dates for fine-tuned analysis. The best known of the gravestone studies was conducted by James Deetz and Edwin Dethlefsen who investigated the religious symbolism of eighteenth - and nineteenth-century Massachusetts. The succession of death’s head, cherub, and urn and willow images on the stones represented a change through time, but the authors further delved into the meanings behind those transformations. In a subsequent study, they considered the spatial dimension of images radiating out from the urban center into the rural hinterland. The strength of these studies (and the many other gravestone studies that followed) is that they consider not only the details of change through time, but also the cultural processes that result in change.
Seriation is a technique that has been used by archaeologists for over 100 years, and despite remarkable innovations in the discipline it is still a valuable tool for interpretation. The technological development, from colored strips of paper to computers, has greatly enhanced the speed and statistical significance of the technique. The lasting importance of seriation relates to its capacity for identifying patterns that may have cultural significance. The challenge for archaeologists is to move beyond the statistics to find the behaviors that generated the patterns.
See also: Sampling Methods, Theory and Praxis; Statistics in Archaeology; Pottery Analysis: Stylistic.
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