The words used to name these spans of time are significant; they demonstrate that this chronological framework comes from a particular theoretical perspective, one associated with the idea of cultural evolution. From a cultural evolutionary perspective, the history of Mesoamerica is also the story of the gradual development of a cultural peak in the Classic period from its initial roots and of a decline after that peak. Each span of time had a particular character and a characteristic level of development. In the Archaic, people lived as mobile hunter-gatherers. The Formative (or Preclassic) was initiated by the advent of the first settled villages of farmers. While some Formative villages had leaders in ritual, war, and other activities, these forms of leadership were not codified into permanent, inherited statuses. With the Classic period, fully developed forms of permanent status, and extreme divisions among people, were realized in cities. The Classic cities collapsed, and in the Postclassic new urban societies emerged that were less impressive, smaller, more secular, or otherwise disadvantageously compared with their Classic predecessors.
These broad time spans, in other words, were not simply periods of abstract time, but rather stages of cultural development. Stages are diagnosed by specific features, like agriculture, pottery, settled villages, hereditary status, and cities. These can be developed at various dates by different peoples. As a result, despite using the same broad categories, researchers working in different sites assigned slightly different dates to each stage. The beginning of the Classic period in the Basin of Mexico was correlated with the maximum development of the great city of Teotihuacan. In the Maya area, it was tied to the first use of writing and calendars on public monuments.
Despite a general move in archaeology away from this early form of cultural evolutionary theory, Mesoamerican archaeology is stuck using an inherited framework of time periods that are really stages. Characteristics that were supposed to define the beginning of a stage are now found to have begun before the initial date of the stage. In the Maya area, the defining feature of the Classic period, written texts and dates on monuments, originated in Late Preclassic times. Archaeologists today treat stage names as labels for arbitrary time segments. Yet the unwanted implication of progress and decline remains embedded in the names for those stages.
From Superposition to Relative Chronology
Scholars often take for granted questions involved in creating chronology: how archaeologists generate dates for events; how these are generalized to time spans; and how theoretical assumptions affect the development of regional chronologies. In order to construct sequences of events, archaeology is dependent on a number of techniques to establish the relative age of material traces: which came first and which followed after. The fundamental principle of superposition, stressed in every introductory archaeology textbook as the key to relative dating, uses an image of layers, one on top of another, corresponding to distinct time periods, with the most deeply buried being oldest and the others following in order. This is, unfortunately, somewhat too simple.
While part of the process of establishing relative chronologies does depend on superposition, superimposed deposits are usually more discontinuous and fragmentary than the layer-cake image presented in textbooks. In many parts of Mesoamerica, major architectural monuments were rebuilt multiple times. The sequence of stages of construction has been a key to establishing local chronology. But fine-grained histories of construction at particular buildings cannot be directly applied elsewhere, even in the same site: the layers superimposed in one place have to be tied to layers superimposed in another.
In the history of Mesoamerican archaeology, the main means of linking together different construction histories was the identification of distinctive types of artifacts, especially styles of ceramics, found in layers at different locations within sites and across regions. Artifacts, especially ceramics, were treated like the “index fossils” of geology, on the assumption that, like natural organisms, styles of pottery had histories with well-defined beginnings and endpoints. Archaeologists are used to things being messier in real life, with pieces of pottery popular at different times becoming mixed together as human beings remodeled buildings and reoccupied previously abandoned terrain. Yet the problem with using artifacts to relate different sites goes further.
In each region where a significant amount of work has been accomplished, sequences have been established for the introduction, growth in popularity, and abandonment of pottery styles. These histories of popularity of pottery, in combination with superimposed architectural sequences, are the fundamental basis for local chronology building. By convention, local units of time derived in this way, called phases, are given names unique to particular sites or regions: Ojochi, Bajío, Chicharras at San Lorenzo, and Cuanalan, Patlachique, Tzacualli, Miccaotli, Tlamimilolpa, Xolalpan, and Metepec at Teotihuacan, for example.
Once such sequences were established in one area, they can be used to help establish sequences in other regions, where items of known relative date (phase) arrived through exchange. Even when items of exactly the types used to create the original sequence are not found, similarities between different regions can be attributed to contact between them, and local sequences coordinated on that basis. The assignment to the period between around 1200 and 900 BCE of pottery with motifs similar to pots of the Gulf Coast Olmec, made in distinct local traditions, is precisely this kind of coordination of different local sequences, not by the presence of an actual index fossil but by the common preference for particular ways of making pottery or other artifacts distinctive of a specific period in time.
This step of correlating different regional sequences raises a problem that Mesoamerican archaeologists continue to grapple with today. The assumption that has to be made is that sites with a shared artifact type or trait are (roughly) contemporaries. This is fine as long as the goal of chronology building is getting places aligned in a common framework of general equivalence on the scale of centuries. This was the procedure of Mesoamerican archaeology through the first half of the twentieth century, when it was dominated by the approach now called culture history. Culture historians aimed to establish the distributions across time and space of different traits, understood as part of sets of traits characterizing distinct cultures. This was viewed as a first step required before more anthropological questions could be formulated and addressed.
The assumption of contemporaneity required to align chronological sequences is more problematic if the questions archaeologists want to explore deal with interaction at a human scale, of the lifetime or generation, where understanding the direction of interaction from one place to another requires finer-grained distinctions in chronology than phases of a century or more. When chronologies are aligned based on shared relative order of innovations, and the necessary assumption of rough equivalence in time of these things, it becomes difficult, if not impossible, to ask or answer questions like, “Did the suite of practices recognized as ‘Toltec’ develop at Chichen Itza, or was the site rebuilt following a Mexican pattern originating earlier at Tula, Hidalgo?” Even within single sites, the correlation of events across different excavated contexts, which may be critical to understanding how the actions of human beings affected different social segments
