James O’Kon is using modern technology and forensic engineering techniques to uncover the mysteries of a vanished Mayan civilization. It began with a pile of rocks in the middle of the Usumacinta River deep in the rain forest between Mexico and Guatemala-the site of an ancient Mayan kingdom,
Approaching the Mayan ruins by dugout canoe, O’Kon, CE ’61, immediately realized the significance of the rock formation.
“That’s a bridge pier!” he declared.
That was in February 1989, O’Kon’s first visit to the Mayan ceremonial center Yaxchilan (pronounced YashSHE- Ian), which flourished during the classic Mayan period between 500 and 700 A.D. Archeologists had been studying the site for more than 110 years, and the mound of rocks had been dismissed as a minor mystery, possibly explained as a once-dry part of the city engulfed by a shifting river.
A former chairman of the forensic council of the American Society of Civil Engineers, O’Kon turned to modern technology to help prove a bridge existed, a technique he has used Professionally. O’Kon is president of
O’Kon and Co., an Atlanta engineering firm that has conducted such forensic engineering investigations as the deadly walkway collapse at the Hyatt Regency in Kansas City, Mo., in the 1980s.
He compiled field information collected at the Mayan site and used computers to integrate archeological studies, aerial photos and maps to develop a three-dimensional model of the site and determine the centerline, discover the location of the bridge abutment and hypothetical construction of the bridge.
O’Kon made a startling discovery: The Mayans built the longest bridge span in the ancient world.
The pre-Columbian bridge was a 600-foot, hemp-rope suspension structure with two piers and three spans built in the seventh century, O’Kon said. Connecting the Yaxchilan ceremonial center in Mexico with its agricultural domain in what is now Guatemala, the bridge had a middle span of 203-feet-the longest span in the world for almost 700 years. In 1377, a bridge with a longer span was built in Europe, O’Kon said.
Link to the “Island City”
The Mayan city was strategically located on high ground. An omega-shaped bend in the river circles the city on three sides, and its only land approach is cut off by steep mountains. Heavy rains made the Usumacinta River virtually impassable from June until January.
“Six months of the year, there is almost 170 to 200 inches of rainfall, and the river is 40 feet above its banks,” O’Kon said. During flood stage, Yaxchilan became “an island city,” he said.
A bridge was essential for the inhabitants of the densely populated city to have year-round access to their domain, their agricultural fields and for commerce, O’Kon said.
The rock pile–12 feet high and 35 feet in diameterwas part of a masonry structure, O’Kon said. Aerial pho tos taken in 1992 revealed the remains of a second support pier on the opposite side of the river, which was almost completely submerged.
Both piers were constructed with an interior of castin- place concrete and an exterior of stone masonry, O’Kon said. “They formed a circle and filled the inside with cast-in-place concrete forming pillars, just like they did their temples and pyramids.”
Identification of the bridge abutment that led to the city’s grand entrance was the “clincher” necessary to reconstruct the complete ceremonial function of the bridge, O’Kon said. A platform situated in an ancient plaza area and located on the centerline of the bridge was a “classic bridge-approach structure,” he said. A stairway leading to the top of the platform and covered in hieroglyphics was also discovered. These stairs were the ceremonial gateway to the city. Carved stone devices were also found, which O’Kon believes were guide- ways for the rope-cable suspension bridge.
“I plugged all of that into the computer,” O’Kon said. “I digitized the maps and put in all the information. Everything lined up-the pillars, the abutments and the ceremonial platform.”
Artist David Morgan, who had been to the Yaxchilan site, drew an illustration of the bridge based on the computer renderings.
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