Complexities of Collapse: The Evidence of Maya Obsidian as Revealed by Social Network Graphical Analysis

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Introduction

Explanations for the florescence and subsequent decline of large urban societies have generated persistent archaeological interest worldwide, for instance the collapse of Minoan urban centres on Crete during the Bronze Age, the decline of urbanism and political integration in the post-Roman period in Europe, and the rise and fall of major urban centres such as Teotihuacan in central Mexico. The decline of urban centres and the depopulation of particular regions in eastern Mesoamerica beginning around AD 800, sometimes termed the Classic Maya 'collapse', has served as an important case for more general models of the rise and decline of urbanism and political integration in the past (e.g. Tainter 1988) and continues to generate new debate (e.g. Webster 2002; Aimers 2007). Models of Maya political reorganisation, as for other global regions, propose causes both environmental (drought, catastrophic volcanic eruptions, hurricanes, anthropogenic environmental degradation) and socio-economic (warfare and invasion, peasant revolt, overpopulation, changing exchange routes) (Webster 2002; Demarest 2004; Chase & Chase 2006; Aimers 2007).

The role of changing trade networks has also been recognised by Maya scholars as a factor that contributed to the transition that characterised the Terminal Classic. Rathje (1973) argued that sites in the Classic 'core' (southern lowlands) were out-competed by settlements on the periphery (for example in the northern Yucatan and eastern Maya area), leading to inland collapse. Webb (1973), in contrast, argued that Maya polities were secondary states that arose in response to an influx of Mexican goods (including obsidian), and that emergence of commercial trade at the end of the Classic period caused a rapid loss of economic viability at inland centres.

Here we examine pan-regional exchange networks by applying graphical techniques from social network analysis (SNA) to chronicle variations in the supply of obsidian to inland and coastal centres. The resulting trends allow us to argue that increasing reliance on coastal trade networks played a key role in the decline of Maya settlements in the western lowlands and contributed to the fluorescence of coastal centres during the Terminal and Postclassic periods.

Maya obsidian exchange

Obsidian is an ideal material to use in reconstructing ancient trade relations. The chemical composition of obsidian recovered in archaeological contexts allows for the original source to be determined with high confidence, provided the regional sources are well understood. This is particularly the case in Mesoamerica, where over four decades of research have resulted in a comprehensive knowledge of the distinctive chemical signatures. In the Maya area of Mexico, Belize, Guatemala, Honduras and El Salvador, obsidian was primarily obtained from three sources located in the highlands of Guatemala, San Martin Jilotepeque (also referred to as Rio Pixcaya), El Chayal and Ixtepeque (Figure 1).

Our regional analysis draws on earlier compilations, particularly Braswell's (2003) synthesis of Terminal (~AD 800-1050), Early Postclassic (~AD 1050-1300) and Late Postclassic (~AD 1300-1520) obsidian for the broader Mesoamerican region. For the Classic period (~AD 250/300-800), data were drawn from earlier summaries as well as primary sources (see supplemental digital material for a complete listing). We have also included new sourcing data (see online supplement) for 70 pieces of obsidian from the Classic and Terminal Classic settlement of San Jose Belize, excavated by Field Museum curator J. Eric Thompson during the early 1930s. San Jose is geographically situated between settlements in the Peten Lakes region to the west and Chetumal Bay to the north-east, both important nodes on routes of transport for obsidian and other goods at contact (e.g. Hammond 1972). Although most of the data included in our analysis were collected by chemical analysis (by)CRF, 1NAA or ICP-MS), we have included visually sourced materials published by other scholars (see Braswell et al. …