Airborne LiDAR, archaeology, and the ancient Maya landscape at Caracol, Belize

Advances in remote sensing and space-based imaging have led to an increased understanding of past settlements and landscape use, but e until now e the images in tropical regions have not been detailed enough to provide datasets that permitted the computation of digital elevation models for heavily forested and hilly terrain. The application of airborne LiDAR (light detection and ranging) remote sensing provides a detailed raster image that mimics a 3-D view (technically, it is 2.5-D) of a 200 sq km area covering the settlement of Caracol, a long-term occupied (600 BC-A.D. 250e900) Maya archaeological site in Belize, literally “seeing” though gaps in the rainforest canopy. Penetrating the encompassing jungle, LiDAR-derived images accurately portray not only the topography of the landscape, but also, structures, causeways, and agricultural terraces e even those with relatively low relief of 5e30 cm. These data demonstrate the ability of the ancient Maya to modify, radically, their landscape in order to create a sustainable urban environment. Given the time and intensive effort involved in producing traditional large-scale maps, swath mapping LiDAR is a powerful cost-efficient tool to analyze past settlement and landscape modifications in tropical regions as it covers large study areas in a relatively short time. The use of LiDAR technology, as illustrated here, will ultimately replace traditional settlement mapping in tropical rainforest environments, such as the Maya region, although ground verification will continue to be necessary to test its efficacy. 2010 Elsevier Ltd. All rights reserved. 1. Introducing LiDAR technology to Maya landscape archaeology Classic Period Maya civilization (A.D. 250e900) evolved within and eventually returned to a jungle-enshrouded tropical environment, making it exceedingly difficult to see the full extent of their settlement and centers. Documentation of settlement is both arduous and incomplete, with virtually all researchers reduced to recording a sample of remains, even within a single site or region. How the ancient Maya distributed and organized themselves over the landscape and how they supported large populations continue to be debated (Becker, 1979; Fox et al., 1996; Iannone, 2002). These issues are made more difficult because the documentation of ancient settlement has been e of necessity e partial. The ability to map an ancient settlement within a dense jungle is hindered not All rights reserved. ., et al., Airborne LiDAR, archa .jas.2010.09.018 only by the covering foliage but also by the amount of funding and time required to undertake the effort. Thus, even the best surveyed sites in the Maya area are only represented by a limited portion of the landscape, meaning that broader interpretations are derived from incomplete samples. The result is continued disagreements over the nature and composition of ancient Maya social structure (Chase et al., 2002), over their political organization (Grube, 2000), and even over the causes behind the Classic Maya collapse (e.g., Webster, 2002). In studying the Maya, researchers have focused mainly on the impressive public architecture that exists within most site epicenters and interpreted their social fabric through hieroglyphic texts located in these areas (Martin and Grube, 2000), leading to a somewhat myopic view of Classic Period society. Settlement archaeology at many of these Maya centers has supplemented these interpretations (Sabloff and Ashmore, 2007), but has generally not succeeded in defining the full spatial layout of sites, in explaining their variable social composition, or in demonstrating how sustainable systems were promulgated. eology, and the ancient Maya landscape at Caracol, Belize, Journal of A.F. Chase et al. / Journal of Archaeological Science xxx (2010) 1e12 2 After 25 years of research andmapping, the archaeological ruins of Caracol, Belize (Chase and Chase, 1987, 2001a; Chase and Chase, 1994b), can be described as the largest known site in the Southern Maya lowlands. As currently understood, Caracol covers almost 200 sq km, spanning most of the Vaca Plateau (Fig. 1); its various parts are linked by a dendritic causeway system embedded in continuous settlement. While agricultural terracing has been documented for Caracol (Healy et al., 1983; Chase and Chase, 1998), the full extent of the modified landscape has been difficult to demonstrate, let alone conceptualize. Yet, several days of airborne light detection and ranging (LiDAR) flyovers of the site, combined with three weeks of post-field processing, yielded results that far surpassedover twoandahalf decades of on-the-groundmappingby revealing images of a massive, modified landscape that ties settlement, roadways, and agricultural terraces together into a complete settlement system. 2. Landscape challenges in building the Maya site of Caracol The LiDAR survey reported here covered themajority of the Vaca Plateau, a level plain located amidst the karst topography ofwestern Belize, where the site of Caracol was built. Caracol and the Vaca Plateau are located at an elevation ranging from450 to 600m above sea level (Chase and Chase, 1987). No running water can be found within the 200 sq km constituting the site, despite the Macal and Chiquibul Rivers being located a short distance to the west and east of the plateau. To solve this challenge, the ancient Maya inhabitants of Caracol constructed a plethora of reservoirs for drinking water (averaging approximately 5 per 1 sq km) and also managed the landscape hydrology through the construction of terraces. The Vaca Plateau receives between 2000 and 2400 mm of rain per year. Temperature ranges from 5.6 to 38.9 Celsius (Johnson and Chaffey, Fig. 1. Hillshaded two hundred sq km LiDAR Digital Elevation Model with an overlay of the boxes are areas shown in more detail in subsequent figures (lower box 1⁄4 Fig. 10; upper boxe is not hilly is referred to as the “Vaca Plateau.”. Please cite this article in press as: Chase, A.F., et al., Airborne LiDAR, archa Archaeological Science (2010), doi:10.1016/j.jas.2010.09.018 1973: 11), sometimes within the same 24 h period of time. Subtropical moist rainforest covers the entire area with a canopy that reaches approximately 25 m in height. In antiquity, the entire Vaca Plateau was heavily occupied by the ancient Maya and integrated into the single urban center of Caracol, characterized by public architecture and thousands of residential groups. 2.1. Earlier mapping techniques at Caracol Mapping the site of Caracol has been a long and protracted effort that has spanned almost 60 years. By looking at the history of the various mapping efforts at the site, the full potential of airborne LiDAR as a technique for recording ancient Maya sites becomes glaringly evident. The earlier mapping techniques used at Caracol were labor-intensive, tedious, and partial e providing nowhere near the amount of information contained in the digital elevation model gained from LiDAR. Knowledge of pre-LiDAR research is important to contextualize and to fully utilize the results of this new technique. The epicenter of Caracolwasfirst reported toBelizean authorities in 1936 because of the discovery of carved stone monuments with hieroglyphs. Archaeological researchwas initially undertaken at the center in the early 1950s, primarily to uncover and record the site’s historic monuments, many of whichwere shipped toThe University Museum in Philadelphia for display. Initialwork at the site produced a description of the hieroglyphs and images on these monuments alongwith amap of 78 structures that documented their location in the site epicenter (Beetz and Satterthwaite, 1981). In the late 1980s, investigations documented the existence of terraces and settlement within an area located 2 km from the site center (Healy et al., 1983) and later demonstrated thatmaize had been one of the crops grown on these constructed terraces (Webb et al., 2004). dendritic Caracol causeway system and the major architectural nodes; the highlighted s from left to right: Figs. 8,6,3,9 and 4; the terrain in the northern part of the figure that eology, and the ancient Maya landscape at Caracol, Belize, Journal of A.F. Chase et al. / Journal of Archaeological Science xxx (2010) 1e12 3 After preliminary seasons in 1983 and 1984, the first formal field season of the University of Central Florida Caracol Archaeological Project took place in 1985. Over the course of subsequent years of investigation, the focus of research has varied extensively, but has always contained elements of archaeological excavation and mapping. As a result of this research (see field reports and publications at http://www.caracol.org), most of the site epicenter has been excavated and stabilized for tourism under the auspices of the project, the Belize Institute of Archaeology, or some combination of the two. Besides the larger architecture in the site epicenter, some 118 residential groups have been investigated by a combination of testing, trenching, and areal excavation. Mapping efforts have resulted in the detailed recording of some 23 sq km of settlement by transit. Additionally, over 75 km of causeways have been documented and approximately 350 ha of agricultural terraces have been intensively mapped. These combined data have led to projected population densities in some parts of the site on the order of 1000 people/sq km (Healy et al., 1983; Chase and Chase, 1998), with an overall population estimate of approximately 100,000 people within a projected area of 177 sq km (Chase and Chase, 1994a:5), making it one of the most populated sites in the Maya lowlands at A.D. 650. This long-term research has led to a detailed view of this ancient city that combines multiple classes of archaeological data with the site’s hieroglyphic texts (Chase and Chase, 2008). Monuments recovered from Caracol provide a history of the site’s dynastic rulers from A.D. 330 through A.D. 859, albeit with some gaps. Archaeological data show that the site was first settled by B.C. 600 and continued to be occupied until at least A.D. 900. The site is perhaps best known for the epigraphically recorded defeat of Tikal, Guatemala in A.D. 562 (Chase, 1991), but it also engaged in warfare with a number of other sites during its 500 years of written history (Chase and Chase, 1989; Chase and Chase, 2003b). As a result of successful warfare, Caracol increased in population and expanded over its landscape at the beginning of the Late Classic Period (ca. A.D. 550), integrating its population by means of an extensive road system that radiated out from the epicenter to distances of up to 10 km (Chase and Chase, 2007). These roads directly connected both pre-existing and purposefully established public space and monumental architecture with the epicenter. The intensity of the agricultural fields that accompanied these expansions was capable of supporting an increased population. The agricultural fields imbedded within the Caracol settlement clearly showed the site to be a “garden city,” concerned with long-term sustainability (Chase and Chase, 1996). 2.2. How survey was undertaken during the Last 25 years of