| 6 January 2007
Ancient footpath retraced using satellite technology
Satellite imagery meshed with video-game technology is allowing University of Colorado at Boulder and NASA researchers to virtually 'fly' along footpaths used by Central Americans 2,000 years ago on spiritual pilgrimages to ancestral cemeteries. The effort has allowed researchers to trace the movements of ancient people in the Arenal region of present-day Costa Rica, who used single-file paths to navigate rugged terrain between small villages and cemeteries over the centuries, said Professor Payson Sheets. The repeated use of the footpaths caused erosion resulting in narrow trenches in the landscape up to 10 feet deep.
The evidence now indicates people re-used the same processional routes for more than 1,000 years, returning to them despite periodic abandonment of villages caused by recurring violent eruptions of the nearby Arenal Volcano, he said. Sheets gave a presentation on the subject at the 2nd International Conference on Remote Sensing in Archaeology held in Rome from Dec. 4 to Dec. 7.
The researchers have traced one processional path from a village on the Caribbean side of northern Costa Rica over the Continental Divide to a cemetery about 10 miles away using infrared satellite images that indicated characteristic signatures of plant growth, he said. The eroded footpaths - some virtually invisible to observers on the ground - collect water that stimulates increased root growth in the vegetation that appears in the images as reddish lines, said Sheets. "This project has been a huge surprise," said Sheets. "Modern technology has allowed for the discovery and study of 2,000-year-old footpaths in the tropics where the ground is covered by thick vegetation and multiple layers of ash from prehistoric volcanic eruptions."
Software originally developed for video games lets the researchers fly along the footpaths at various altitudes, directions and tilt angles and zoom in on particular landscape features, said Sheets. The team has been able to pinpoint sources of stone used to construct elaborate graves and to confirm springs used for water during ritualistic feasting ceremonies at the cemeteries that lasted for days on end. "We now know some villages adapted to volcanic eruptions at least four times, retracing the same footpaths to their cemeteries," he said. "We would never have known this without the imagery, and it indicates to me they had a deep need to contact and re-contact spirits of dead ancestors by attempting to access the supernatural."
Images of the footpaths were made by various NASA satellites and aircraft and by a commercial satellite known as IKONOS. IKONOS has a resolution of less than one meter and is equipped with infrared sensors that can peer through deep jungle foliage. The team used computer software known as TerraBuilder, a 3-D terrain construction application.
The footpaths lead from villages occupied from roughly 500 B.C. to 600 A.D to dozens of small cemeteries in the region, where archaeological evidence indicates visitors cooked, ate, drank, slept and ritually smashed pots on the stone slab-covered graves to commemorate the deceased, he said. The 3-D visualization project allows users to experience the viewpoint of villagers as they strode out of narrow, subterranean footpaths into the graveyards, a process he likened to "emerging from a tunnel," he said. Subsequently, more complex prehistoric cultures in the region took the concept a step further by developing massive, sunken pathways with entryways wider than soccer fields that connected satellite communities with regional centers as a way to "magnify monumentality," he said.
Source: EurekAlert! (2 January 2007)
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