Largest ancient dam built by Maya in Central America uncovered

Washington - During recent excavations, sediment coring and mapping at the pre-Columbian city of Tikal–a paramount urban center of the ancient Maya – a multi-university team led by the University of Cincinnati have identified new landscaping and engineering feats, including the largest ancient dam built by the Maya of Central America.

That dam – constructed from cut stone, rubble and earth – stretched more than 260 feet in length, stood about 33 feet high and held about 20 million gallons of water in a man-made reservoir.

These findings on ancient Maya water and land-use systems at Tikal, located in northern Guatemala, sheds new light on how the Maya conserved and used their natural resources to support a populous, highly complex society for over 1,500 years despite environmental challenges, including periodic drought.

Starting in 2009, the UC team was the first North American group permitted to work at the Tikal site core in more than 40 years.

According to Vernon Scarborough, UC professor of anthropology, “The overall goal of the UC research is to better understand how the ancient Maya supported a population at Tikal of perhaps 60,000 to 80,000 inhabitants and an estimated population of five million in the overall Maya lowlands by AD 700.”

He added, “That is a much higher number than is supported by the current environment. So, they managed to sustain a populous, highly complex society for well over 1,500 years in a tropical ecology. Their resource needs were great, but they used only stone-age tools and technology to develop a sophisticated, long-lasting management system in order to thrive.”

Water collection and storage were critical in the environment where rainfall is seasonal and extended droughts not uncommon. And so, the Maya carefully integrated the built environment – expansive plazas, roadways, buildings and canals – into a water-collection and management system.

At Tikal, they collected literally all the water that fell onto these paved and/or plastered surfaces and sluiced it into man-made reservoirs. For instance, the city’s plastered plaza and courtyard surfaces and canals were canted in order to direct and retain rainwater runoff into these tanks.

In fact, by the Classic Period (AD 250-800), the dam (called the Palace Dam) identified by the UC-led team was constructed to contain the waters that were now directed from the many sealed plaster surfaces in the central precinct.

It was this dam on which the team focused its latest work, completed in 2010. This gravity dam presents the largest hydraulic architectural feature known in the Maya area. In terms of greater Mesoamerica, it is second in size only to the huge Purron Dam built in Mexico’s Tehuacan Valley sometime between AD 250-400.

“We also termed the Palace Dam at Tikal the Causeway Dam, as the top of the structure served as a roadway linking one part of the city to another. For a long time, it was considered primarily a causeway, one that tourists coming to the site still use today. However, our research now shows that it did double duty and was used as an important reservoir dam as well as a causeway,” said Scarborough.

Another discovery by the UC-led team: To help purify water as it sluiced into the reservoir tanks via catchment runoff and canals, the Maya employed deliberately positioned “sand boxes” that served to filter the water as it entered into the reservoirs.

“These filtration beds consisted of quartz sand, which is not naturally found in the greater Tikal area. The Maya of Tikal traveled at least 20 miles (about 30 kilometers) to obtain the quartz sand to create their water filters. It was a fairly laborious transportation effort. That speaks to the value they placed on water and water management,” said Nicholas Dunning, UC professor of geography.

According to archaeologist Kenneth Tankersley, UC assistant professor of anthropology, “It’s likely that the overall system of reservoirs and early water-diversion features, which were highly adaptable and resilient over a long stretch, helped Tikal and some other centers survive periodic droughts when many other settlement sites had to be abandoned due to lack of rainfall.”

These findings are scheduled to appear this week in the Proceedings of the National Academy of Sciences (PNAS).