Introduction

Least Cost Path Analysis: An Archaeological Application in Mesocamerica

David Lewis, Master Student, Fish, Wildlife & Conservation Biology

Florencia Pezzutti, Doctoral Student, GDPE (Anthropology)

Introduction: Prehispanic Roads

Prehispanic built environments are an expression of how humans created and defined spaces on the landscape. The built environment documented at the site SA1 in the Lake Pátzcuaro Basin, Michoacán, Mexico, has provided evidence of three levels of interaction: intra-household, intra-site, and inter-regional. Here we analyze the road, paths, and trail systems documented at Sacapu Angamucu, and we compared them to hypothetical routes at multiple scales to test the potential use of GIS least-cost path analysis as a prediction tool of prehispanic routes at a regional and local archaeological level.

Archaeological sites are spaces on the landscape usually represented as a point or polygon on a map, and as such they articulate with other sites and with their contexts via trails, roads, and routes. Some well known Mesoamerican examples of roads are the Inca calzadas (raised roads) and the Mayan sacbes. Thus, prehispanic routes documented in the archaeological record have an significant importance to understand past human interactions, since they can provide information regarding commercial and exchange relationship between two sites or regions (Garcia Martinez 2006:25).

For archaeological research, and even in today’s society, trails, roads, and routes are significant because they can define the way people organize and divide their social space. Ancient trails, roads, and routes have been the cultural, economic, and diplomatic veins through which people, exotic goods, traditions, ideas, knowledge, economic trade, and military troops flew dynamically across diverse landscapes (Fournier 2006:27). With the improvement of different technologies and techniques, such as in the field of Remote Sensing, archaeologists interested in documenting ancient prehispanic trails, roads, and routes have used aerial photography, satellite imagery, and archaeological survey.

In some regions of Mesoamerica, as in other European colonized regions of the world, prehispanic roads kept being used during the European colonial period, and have been modified to today’s modern roads. Even though modern development has either altered or completely changed prehispanic roads, there are still regions in Mesoamerica where it is still possible to observe and document intact prehispanic roads in the archaeological record. Such place is the archaeological site of SA 1 in the Lake Patzcuaro Basin, in Michoacán, Mexico.

Image information left to right: Tuxpan Canvas. Anthropology Museum, Xalapa, Veracruz , XVI century (Arqueologia Mexicana 2006); Pochteca (maket people) mexicas. Florentine Codex, lib.IX,f.8r (Arqueologia Mexicana 2006)

The Lake Patzcuaro Basin: An introduction

The Lake Pátzcuaro Basin (LPB) was the geopolitical core of the Purépecha Empire at the time of European Contact (A.D. 1520) with a dense population, centralized settlement system, socially stratified population, and an engineered environment (Fisher 2005). The LPB has long been recognized as a Mesoamerican “core” (Palerm 1955) region; however, it is one of the most understudied areas. The Purépecha Empire was contemporary and enemy to the Aztec Empire during the Late Postclassic Period (A.D 1350-1521). The Purépecha Empire controlled a vast territory of west central Mexico, delimited to the north by the Lerma River, to the South by the Balsas-Tepalcatepec River, to west the Pacific Ocean, and most importantly, to the east, it shared an eastern frontier with the Aztec empire. A buffer zone, consisting of fortifications characterized this fixed, yet, permeable boundary of two opposing imperial powers. The capital of the Purépecha Empire was Tzintzuntzan, under which a complex of socio-political polities were consolidated under a State and later it became the administrative, religious and political control of the Purépecha Empire.

The Lake Pátzcuaro Basin terrain consists of a rugged and broken topography that increases from 2,050 m at the lakeshore to a total of 3,200 m, once it reaches the outskirts of the Empire’s periphery (Pollard 1991:169). Previous study on prehispanic trails, roads, and routes for the LPB was conducted by Gorenstein and Pollard (1991:169-185). Their archaeological research was mostly based on ethnohistorical information, and did not emphasize too much on the archaeological data of roads, paths and canoe routes. One of the most important and used ethnohistorical accounts for this region is the “Relación de las Ceremonias y Ritos y Población y Gobernación de Michoacán”, which describes the protohistoric period and the formation of the Purépecha State and Empire. The Relación de Michoacán has plenty of protohistoric descriptions of landscape perceptions and roads around the lake basin region. The Relación de Michoacán is believed to have been written by a Spanish emissary sometime between 1539 and 1541 (Glass, 1975 in O‘Hara 1993). The document was created to understand and explain the history, functioning, lifeways, customs, and religion of the Purépecha people, prior to and during the European conquest. Based on this ethnohistorical document, Gorenstein and Pollard (1991:170) present three types of communication routes in the Lake Pátzcuaro Basin: 1) a road around the lake “camino cabe la laguna” which linked all the settlements in the shorelines; 2) Canoe routes, which was a common way of transportation of goods and convey information during war times; and 3) Trails, roads and routes descending from the higher slope elevations, away from the lake basin, that connected distant sites with the circuit lake route. These three types of routes were based on indicators resulting from the relationship between the archaeological settlements, in terms of a) their role in the Lake Pátzcuaro Basin and b) the accessibility or reachability of the site in terms of presence or absence of direct linkages between nodes (settlements).

Fray Pablo de Beaumont (Cronica de Michoacan, ca. 1550) (Arqueologia Mexicana 2006).

An Archaeological Application of Least Cost Path Analsys: Introduction

This project presents a geographic information system (GIS) based method for the identification of archaeological road, routes, and passages significant for their trade and communication value during the Late Postclassic (A.D.1350-1520) in the Lake Pátzucaro Michoacán, Mexico. The project considers the cost of traveling based on topography. The project methodology utilizes the least-cost path algorithm within GIS framework to obtain the trails, roads, and routes and compared them with recently documented archaeological routes, roads, and passages in SA1 archaeological site, a recently discovered urban late Postclassic site. The path location algorithm considers the cost of slope degree and accumulated cost over a certain distance.

As previous archaeological studies (Morgan 2008) have shown, this project will attempt to show the efficacy of using archaeological features (socio-spatial zones) with terrain modeling (slope) to help reconstruct prehispanic trading and communication routes, roads, and trails in the context of social and ecological factors.
We apply the least cost path analysis, to develop an optimal model which explores the patterns of communication between the eastern obsidian mines regions (periphery) and the west (the core of the Purépecha Empire in the Lake Pátzucaro Basin. The output GIS model can provide the baseline for considering factors that affected the communication at the regional, local, and intra-site scales, but it also presents the potential value of GIS as a cost efficient method to predict routes, roads, and trails in the archaeological record.

Assumptions

People coming from east to west routes are coming from either the periphery of the Purépecha Empire where the most important obsidian mines are located. These mines are located in the southeastern portion of the Cuitzeo Lagoon,located northeast of the Lake Pátzcuaro Basin. The obsidian mines being considered for this project are: Maravatio and Ucareo/Zinepacuaro. These mines have notoriously distinctive types of obsidian. Obsidian was a desirable commodity among the Purépecha elites. Therefore, the communication routes between the obsidian mine zone and the capital of the Purépecha Empire, Tzintzuntzan, is a significantly important route we explore in this project. These towns were conquered by the Purepecha during the Purepecha Empire expansion and were of great importance due to the obisidan that could be extracted for consumption in the Lake Patzcuaro Basin region.

People coming from east to west routes are coming to either pay tribute, trade, and or communicate.

These people travel through already established and familiar roads, which have remained in the archaeological record, but have only been partially mapped and documented. Some of these already established routes have continued to be used and are today’s modern roads in the lake basin region.

In the context of a mountainous environment, we assume that at high elevations, or with steep slopes the cost of traveling is very high in terms of energy expenditure for traveling on foot.

Obisidan tools and debitage collected from SA1 archaeological site (Fisher and LORE-LPB archaeological project)