Applying GIS tools to define prehistoric megalith transport route corridors: Olmec megalith transport routes: a case study

Abstract

Applying spatial data management and analytical tools is an accepted method for investigating potential settlement patterns. This study applied Geographic Information System (GIS) technology to the study of Preclassic Olmec megalith transport in Mesoamerica. The GIS slope gradient tool was used to identify potential transport corridors with gradients of less that 1:10, which defines the limit of human effort needed to control these stones as demonstrated in ethnographic and replication experiments by various researchers. These outcomes were also used to refine transportation methods and likely start points that would be used to cross lowlands near to the San Lorenzo centre of Olmec society.

Introduction

Stone use is enduring evidence of the industry, enterprise and resource of prehistoric cultures. Transporting large stones or megaliths was a pivotal part of this prehistoric industry. The methods and routes that were chosen for this undertaking continue to be the subject of debate and have given rise to considerable speculation. The sources for stones were often distant from their final position and the routes that were used to retrieve the stones traversed difficult terrain or open seas (Hazell, 2011). The sources and routes often bypassed, what to modern eyes, may seem to be suitable stones and more convenient sources; so adding significant logistical issues to the problem of stone retrieval.

A limited material and often fragmented, archaeological record, limits any endeavours to determine the methods and routes that were used to undertake these monumental activities. To overcome this, ethnographic examples are often cited (Ayres and Scheller, 2001; Dillon, 2004; Heyerdahl, 1958; Souden, 1997) and replication experiments (Atkinson, 1960; Ayres and Scheller, 2001; Richards and Whitby, 1997; Van Tilburg, 1995) are also used as a basis for research.

Experiments have limitations because the conditions under which they were conducted may differ substantially from those encountered by ancient cultures and are unlikely to replicate all aspects of this complex undertaking. In Mesoamerica transporting megaliths involved technological knowledge, logistical expertise (Diehl, 2007) and significant resources to overcome terrestrial features and – according to some – oceanographic hurdles (Coe, 2000; Stuart, 1993; Velson and Clark, 1975). While some aspects of replication experimentation are inappropriate it is still possible to use human physical capabilities, identified in replication experiments and corroborated by ethnographic observations. These sources have been adopted as part of Geographic Information System (GIS) analyses in order to identify viable and sustainable land route options and transportation methods (Ayres and Scheller, 2001; Erasmus, 1965; Heyerdahl, 1958; Horvath and Finney, 1976; Irwin et al., 1990; Richards and Whitby, 1997; Schiffer and Skibbo, 1987).

This Mesoamerican investigation of Preclassic (1800 BC–400 BC±) Olmec society megalith transportation includes these and other challenges including limited field survey access to the large areas involved and securing sufficient funds to study such an extensive site; therefore another technique was required to study this geographically extensive transport problem. The focus of this study was on land transport of megaliths used in sculptures known as the Colossal Heads, ten of which were found at San Lorenzo. Large numbers of stones, most weighing between 6 and 26 tonnes, were moved to this area and also to La Venta, which was another major and later Olmec complex. For this research a mean mass of twenty tonnes has been adopted.

This paper documents our use of GIS technology to determine whether viable land routes and methods, which comply with human power capability calculations and terrain conditions, can be established. The outcomes derived from this work were able to show that ancient Olmec could have transported stones by land in contrast to the more favoured open water and river routes. However, it went further by defining some transport methods because ground conditions also precluded the use log rollers, sleds and wheeled vehicles, even though the wheel was known to Olmec society, as evidence of wheeled toys demonstrate (Charnay, 1974).

The distances involved are considerable, and the terrain is challenging, with swamps, floodplains and rivers, many of which are seasonal. From their source near Cerro Cintepec in the Tuxtla Mountains to their final destination at the Preclassic centre of San Lorenzo is a straight line distance of around 80 km across this difficult landscape (Coe, 2000: 68). Importantly gradient analysis using the GIS software allowed us to establish a potential transport corridor from which the Olmec could begin to cross the lowlands. Transportation methods were also defined by gradient and related road structures needed to support this activity. For this reason, our GIS matrix included soil types and their distribution, as existing archaeological evidence shows significant earth structures associated with the San Lorenzo complex.

Olmec society had a significant sphere of influence and is often described as the “Mother culture” (Benson, 1981; Benson and de la Fuente, 1996; Coe, 1965, Coe, 1981; Coe and Diehl, 1980; Cyphers, 1996; Puche et al., 1996). Archaeological surveys and excavation projects have shown that Olmec society built complex centres at different sites during their florescence. They rose in prominence in about 1500 BC and then declined again by 600 AD (Coe, 1965, Coe, 1970, Coe, 2000; Coe et al., 1967; Coe and Diehl, 1980; Stirling, 1943, Stirling, 1965). Their “heartland” dominated much of what is now known as Veracruz State in Mexico.

The “Olmec heartland”, which is accepted as the Olmec sphere of social, political and economic influence, was an area of some 16,000 km². The Olmec traded in obsidian and jade, neither of which occur naturally around Olmec centres. Trade pathways, while suitable for precious mineral trade, would not necessarily suit megalith transport; however trade in precious materials suggests that regularly used pathways may have existed during Olmec times.

Olmec society moved many large stones for stelae, altars or thrones and sculptures. Amongst the hundreds of stones that were used for different purposes, the largest known stone was La Venta 1, which weighed about 40 tonnes (Clewlow et al., 1967; Clewlow, 1970). At San Lorenzo near Tenochtitlan extensive raised platforms, numerous mounds, stelae, altars and stone sculptures, known as Colossal Heads, have been found (Benson and de la Fuente, 1996; Clewlow et al., 1967; Clewlow, 1970, Clewlow, 1974; Pohorilenko, 1996; Stuart, 1993).

Most of the seventeen Colossal Heads weigh between 6 tonnes and 26 tonnes. They vary in height from between one and a half metres to nearly 3 m; their circumference varies from just over 3 m up to nearly 6 m (Clewlow et al., 1967) and each stone has a human face carved into it. The distinctively individual features of each stone's carved face, arguably links each of the Colossal Heads to an Olmec ruler (Clewlow et al., 1967; Stirling, 1965). The stones are generally accepted as being sourced near the foothills of the Tuxtla Mountains (Williams and Heizer, 1965). Ten of these stones have been found on or in gullies on the San Lorenzo Plateau. Some heads are believed to have been reused altar stones, perhaps pointing to their value and linked to difficulties in acquiring these stones (Cyphers, 2006; Porter, 1990).

Any direct land route would encounter swamps and perennial floodplains (INEGI, 1985, INEGI, 1986, INEGI, 1999). The existence of these natural obstacles endorsed argument for water transport of these megaliths (Cyphers and Ortiz, 2000; Cyphers and Zurita-Noguera, 2006, Tamayo and West, 1964).

It is known that the Olmec used canoes for trade, whether these would be suitable for megalith transport is uncertain (Anawalt, 1992; Callaghan, 2003; Dillon, 1975; Edwards, 1978). Analyses of waterborne options highlighted serious limitations of the most likely watercraft known at the time these stones were moved. A study of rafts and multi-hull dugout canoes (Hazell, 2003), based on performance observations, structural integrity, and stability under significant loads, combined with human capability studies (Baumeister, 1967; Hazell, 2011; Henderson and Haggard, 1925; Horvath and Finney, 1976; Severin, 1988) of maximum human power and sustained effort (Doran, 1971, Doran, 1978; Edwards, 1965; Kent, 1958; Ling, 1970; Muckle, 1975; Walton, 1906; West, 1961) has questioned whether waterborne options for moving these megaliths would be viable or reliable. Even if the Olmec did use water transport for moving these stones from their source to final destination, establishing land based pathways from their source points in the foothills of the Tuxtla Mountains to suitable water staging sites would still require analysis of large tracts of land.

With the considerable area involved and limited access, the use of GIS allowed a viable, cost effective research methodology for this aspect of the research.

The region between the source in the Tuxtla Mountains and final destination on the San Lorenzo Plateau is characterized by many rivers, seasonal swamps and floodplains which are subject to inundation during wet seasons or are permanently under water (Cyphers, 2008; Cyphers and Ortiz, 2000). The use of land routes to avoid these constraints during drier months, or using strategies to overcome inundated areas, has already been suggested (Cyphers, 2006). Besides these landform challenges, manpower needs must be considered for transportation methods.

Gradient is an important constraint when moving large stones. This constraint will limit the ability of humans to move the Colossal Heads across the landscape, irrespective of whether these megaliths are being hauled down hill, where there is a need to control their descent, or when they are being hauled uphill to isolated pockets of higher ground to avoid uncertain conditions. Gradient also plays an important part in the final stages when hauling them onto the San Lorenzo Plateau itself. Therefore slope gradient analyses were used to link pathways from the higher ground to potential routes across the low country.