Radar Reveals Canals at Mayan Agricultural Centers

Date June, 1980

Radar images indicated the presence of a network of canals in areas surrounding Mayan population centers. With the development of aerial radar mapping, it became significantly easier for scientists to screen large, unexplored areas for the presence of human-made structures.

Locale Belize; Guatemala

Key Figures

• John Lloyd Stephens (1805-1852), American attorney, explorer, and minister to Central America who wrote extensively about his explorations of the Mayan ruins
• Frederick Catherwood (1799-1854), English illustrator and explorer
• Diego de Landa (1524-1579), Spanish Franciscan priest who was appointed bishop over the Yucatán

Summary of Event

Like the Aztec and Inca civilizations that had been discovered and documented in Central and South America by explorers Hernán Cortés and Francisco Fernández de Córdoba in the 1500’s, the Maya were contacted as early as 1502. After the plundering of the Aztec capital Tenochtitlán, near present-day Mexico City, in 1521, the Spanish conquistadors turned their attention south. Cortés sent one of his captains, Pedro de Alvarado, with a small force of Spanish soldiers and a contingent of twenty thousand native troops, and shortly thereafter, Guatemala and San Salvador were under Spanish rule. In addition to the diseases that were introduced to the continent, the conquest also involved the destruction of the Indian identity. This reached its zenith on July 12, 1562, with the destruction of an entire Mayan library of pictographic books and codices by Friar Diego de Landa. To date, only four of these volumes are known to remain.

Clashes between the Spanish and various indigenous tribes occurred throughout the entire Central American region and lasted almost twenty years. What was revealed to the Europeans was a vast landscape of empty cities. It was apparent that the conquered Mayan nation was a shadow of its former self.

In 1840, these empty ruins were brought to light again by the explorations of John Lloyd Stephens and Frederick Catherwood, who documented the remains of eight ruined cities. These cities included Quiriguá, Copan, Palenque, and Uxmal. The region was lightly populated, with large areas of rain forest being systematically cut down and burned to provide growing space and fertilizer for several years of farming. The practice, commonly called slash-and-burn farming, was being carried out by the indigenous population. This practice is characteristic of present-day subsistence-level farming in tropical rain forests.

This type of agriculture, however, could not have supported the estimated 14 million people that had occupied those now dead cities. The Aztec in central Mexico used more advanced techniques to include chinampas (artificial islands) and irrigation, while in South America, the Inca practiced terracing and fertilization. At that time, however, there was little evidence found in Central America of these advanced horticultural techniques. What Stephens and Catherwood did discover was a complex system of cenotes (reservoirs) as well as artificial aguadas (wells). Farmers used these wells, not knowing that they were constructed earlier. Dry-season excavations of the wells found evidence that they were human-made. A survey of one locale revealed more than forty such constructions. It was not known who built these structures and why they were abandoned.

Part of the mystery is that the Mayan civilization began its decline about 900 c.e., leaving behind its cities and petroglyphs. Several theories say that the culture declined either as a result of conquest by neighboring nations or as a result of famine causing the Maya to migrate and merge with one of the other cultures. Until the late 1970’s, the prevailing thought was that a climatic change caused a drought, with the slash-and-burn type of farming unable to support a large population under those extreme conditions. It became apparent that the lack of any large-scale land surveys, combined with the limited fieldwork done on nonurbanized areas, would continue this debate over how a large Mayan population had supported itself.

From October, 1977, until August, 1980, the National Aeronautics and Space Administration (NASA) made available an airborne, side-looking radar to begin detailed mapping of northern Belize and northeastern Guatemala. The radar was designed originally for the radar mapping of the surface of the planet Venus, but a more suitable application appeared to be the mapping of the swamps and jungles that make up two-thirds of the Mayan territory. This would allow researchers to see through the tree cover and marshland and for the first time allowed a large region to be investigated for the presence of human-made structures. The focus of this mapping was on the site of Tikal, the largest site identified with Mayan culture.

The radar provided an image that varied from 10 to 21 kilometers in width, with a resolution of 20 meters. Many of the large buildings cast shadows and the large, flat surfaces reflected the radar, showing up as spots of light. What surprised the researchers was the appearance of intricate patterns of lines in areas known to be swamps. Because these lines were confined to low-lying land, the immediate label given to them was canals, as used for either transportation or drainage. If further examination proved this correct, then it meant that instead of subsistence-level agricultural practices, the Maya had developed a more sustainable form of farming.

The next step was confirmation of these data with on-site excavations. Ground examination indicated a system of raised fields with the canals acting as drainage conduits, therefore correlating with the information gathered by aerial imaging. In addition, an excavation found canals one meter wide separating fields that were three meters square. Because of the radar’s resolution, however, these features remained for the field archaeologist to interpret. It was found that many of these fields were artificially raised to make them more suitable for agriculture. The Maya may have utilized these raised fields to grow a variety of food and fiber plants. Analysis of pollen and other plant debris indicates the presence of corn, cotton, and amaranth. Unfortunately, the presence of these plants can be explained by either human cultivation or the self-reproduction of wild species. Water lilies are also associated with these raised areas. Studies have shown that these plants provide a good mulch for the crops that could have been grown on these elevated islands.

The radar could not discriminate between ancient and modern structures, as such; railroads, highways, airstrips, and natural geologic structures were picked up also. Of additional interest, however, is what appears to be the presence of some paved areas, possibly roads built by the Maya.

Significance

The radar land-mapping technique altered the way archaeology is viewed and added much to existing knowledge about the Mayan civilization. Traditionally, archaeology has been thought of as a science requiring laborious methods and extensive human resources to accomplish the work of literally uncovering past civilizations. With this new tool of aerial radar mapping, however, it became significantly easier for researchers to screen large unexplored areas for the presence of human-made structures. The past image of archaeology involving hundreds of laborers removing debris was replaced by the image of technicians poring over airborne images.

Knowledge of the Maya also changed. It was never fully understood why the Maya would build large cities in what appeared to be vast swamps. Because these lands, when drained, could provide a stable agricultural base, the Maya might have considered this land the most valuable. The extent of the network of canals indicates a high degree of centralization; an estimated 2,500 square kilometers (or 250,000 hectares) of land in Belize and the Peten region alone were subjected to this type of hydraulic engineering.

The work was not easily accomplished, as the indigenous culture did not have the wheel, any draft animals, or iron tools prior to the arrival of Western explorers. This means that all the work was done manually, with stone tools and baskets to move the debris. A research team tried to replicate the construction of a raised field using tools and techniques that the Maya would have employed. From this work, the team estimated that it would have taken a minimum of 500,000 laborers to build the fields in fifty years. Another possibility is that the system of canals may have evolved during the life span of this culture. Like all Mesoamerican cultures, the Mayan culture had at its base the farmer. It is reasonable to assume that during the height of the society, as many as 10 million people were working the land.

This revelation also helped scientists to reevaluate how the agricultural capabilities of the tropical rain forest are viewed. The practice of slash-and-burn farming bankrupts the fragile soil, whereas the use of silt and aquatic plants dredged from those canals can act to build the topsoil, add additional nutrients, and lead to more productive farming practices. Some observers have expressed hope that the people of Central America will take advantage of the new knowledge gained in the study of the Maya. By the early years of the twenty-first century, a shift appeared to be starting, with the training of native farmers in a more regenerative style of agriculture. This is likely to be the most lasting impact of the discovery and study of the canal systems of the Mayan civilization.

Bibliography

Adams, Richard E. W., Walter E. Brown, Jr., and T. Patrick Culbert. “Radar Mapping, Archaeology, and Ancient Maya Land Use.” Science 213 (September 25, 1980): 1457-1463. Outlines the discovery of waterways through the use of aerial radar. Excellent bibliography covers the work done by previous investigators studying Mayan land use.

Demarest, Arthur. Ancient Maya: The Rise and Fall of a Rainforest Civilization. New York: Cambridge University Press, 2004. Accessible work details the ecological bases and volatile political history of the civilization.

Hunter, C. Bruce. A Guide to Ancient Maya Ruins. Norman: University of Oklahoma Press, 1974. Interesting, basic resource on Mayan cities and culture. Careful reading reveals the misconceptions that were long prevalent concerning Mayan agriculture.

Ivanoff, Pierre. Maya. New York: Madison Square Press, 1973. Photographic record of fifteen different Mayan cities. One of the best books available for readers interested in major cultural landmarks of the Maya.

Stephens, John L. Incidents of Travel in Yucatan. 2 vols. Reprint. Mineola, N.Y.: Dover, 1963. Provides an excellent firsthand account of the rediscovered ruins on the Yucatán Peninsula. Includes drawings.

Turner, B. L., II, and Peter D. Harrison. “Prehistoric Raised-Field Agriculture in the Maya Lowlands.” Science 213 (July 24, 1981): 399-404. Discusses at length the excavation of a Mayan settlement in the Belize lowlands.