The Lost Secrets of Maya Technology

by James A. O'Kon

  The second exploration of the site was carried out in March 1993, working under the auspices of a film permit from the Mexican Instituto National de Anthropologia y Historia (INAH). The engineering team was accompanied by a public broadcasting film crew under the direction of archaeologist Dr. Nicholas Hellmuth. The mission of the film crew was to photograph the engineering investigation related to the hypothesis of the Maya bridge. The crew set out from the Mexican river port of Fonterra. Professional outfitters transported the team in large pontoon boats. We traveled down to the city of Yaxchilan and set up our camp in the same location used during the first visit.

  Figute 10-6: Photo of bridge suspension rope mechanism. Note “wear grooves” in circular support. Author’s image.

  The procedures for surveying the river and the bridge structure were planned in advance of the visit. The area of the river adjacent to the bridge location was visually surveyed and photographed above and below the water level. Field sketches were developed of the alignment and geometrical configuration of the salient elements of the bridge structure adjacent to the river. Additional bridge mechanisms were encountered, investigated, and photographed (Figure 10-6). When the survey was completed and analyzed, the overall configuration of the bridge, its method of construction, and its operating mechanisms became apparent. Field sketches were developed detailing the geometry of the structure and the nature of the materials of constructions of the bridge.

  Maya engineers had constructed a long-span bridge using the optimum high-strength materials available for construction. They configured masonry and composite, cast-in-place concrete, high-strength henequen rope cables, and timbers into the construction of a three-span suspension bridge. The following is a summary of our structural hypothesis that was developed and sketched in the field.

  The Structural Concept of the Bridge

  The bridge was hypothesized to be a three-span, rope cable suspension structure. The bridge spanned from the south bank of the river to the south pier; the long middle span was supported by the two intermediate composite stone and concrete piers (south and north pier) located in the river; the bridge spanned from the north pier to the north embankment. The bridge terminated at the north embankment anchorage. The bridge walkway was located at the elevation of the Grand Plaza.

  South Bridge Pier

  The south bridge pier is located 25 meters from the river’s edge. The remains of this pier extended 3 meters above the water level and have a base dimension of approximately 10 meters. The structure is constructed of a facade of worked stone with an interior in-fill of cast-in-place concrete.

  North Bridge Pier

  The center of the north bridge pier is 63 meters in distance from the center of the south bridge pier. This distance of 63 meters equaled the length of the center span of the suspension bridge The remnants of the superstructure, which were located by aerial photography and verified by divers at the time of the 1993 survey, were almost completely under water at the time of the survey (Figure 10-5). The foundation for the tower was formed by large, flat stones, which were laid directly on bedrock. The diameter of the pier was measured to be 10 meters, the same dimension as the south pier.

  Bridge Abutments

  Bridge abutments that terminated at each end of the bridge were located at the south and north ends of the bridge. The abutments provided anchorage for the rope cables and support for the walkway. The force of the water flow has degraded and displaced the bridge abutments. The embankments founded on the soil of the riverbank were undermined, collapsed, and then dispersed downstream by the scouring effect of the swiftly flowing water.

  Bridge Mechanisms

  Several uniquely carved stone mechanisms were observed downstream from the piers (Figure 10-6). The mechanisms consist of two large, parallel, carved-stone surfaces connected at midpoint by a rounded concave element. Observations indicated smooth, circular grooves in the mechanism apparently caused by wear due to the friction from the rope cable suspension system; the rope cables were supported by this mechanism. This device is similar to rope cable guideways used in modern bridge construction and would have been used as the suspension rope keepers for the bridge piers and anchorage guides at the abutments.

  The Grand Stairway

  Observations along the riverbank indicated the ruins of a 10-meter-wide stairway that led up from the south riverbank to the Grand Plaza. The stair was sited directly to the west of the bridge.

  Archaeo-Engineering Synthesis and Analysis of Data

  The site visit of 1993 yielded a plethora of critical information that contributed to the data for reconstructing a virtual, computer-based bridge structure and a three-dimensional fly-through of Yaxchilan, the Usumacinta River, and the Maya bridge. Field data from the expeditions, aerial photography, remote sensing, and the historical evidence were assessed in my office in Atlanta, Georgia. The research efforts were synthesized, and the bridge was reconstructed using forensic engineering techniques and digital tools. Computer modeling and simulation techniques verified the centerline location of the bridge, the geometry of the bridge structure, and the topography of the Grand Plaza.

  The 1993 site visit, which was primarily dedicated to structures at the level of the river, did not survey structures on the plaza level. However, chance encounters led to vital information that we had totally overlooked. It was logical that a grand bridge would have a significant entrance structure located on the Grand Plaza, and we had not searched the plaza level for a structure that would fit the description of a monumental bridge approach structure aligned with the centerline.

  In her book, Yaxchilan: The Design of a Maya Ceremonial City, archaeologist Dr. Caroline Tate describes each individual structure along the river side of the plaza and includes a reference to the ruins of the bridge pier, which she considered to be the remains of a flood-ravaged structure lost to the river. However, she actually identified the bridge approach structure on the Grand Plaza in her description of Structure 5. This long stone platform is parallel to the river and plaza. It has a hieroglyphic stairway facing the Grand Plaza and is described by Dr. Tate as “a long low platform paralleling the axis of the main plaza.” She notes that no trace of masonry superstructure has been found on the top. To the rear of the building is a narrow soil esplanade with a steep descent into the river. It was obvious; she was describing the configuration of a classic bridge approach structure.

  The entrance facade of Structure 5 consists of a stairway made of six risers constructed of 188 individual stone blocks carved with hieroglyphics. Dr. Tate also describes the ruins of a stairway down to the riverbank adjacent to Structure 5. She writes that “in ancient times someone entering there would have passed between the structures as a gateway to the city.” Dr. Tate provides a clear description of an elevated platform, which served as a grand entrance to the city. Structure 5 combined the flow of travelers arriving by boat and gaining access to the plaza via the broad river stairway with the pedestrians crossing the bridge to develop a monumental entrance to the Grand Plaza.

  The description of Structure 5 on the Grand Plaza was presented in Dr. Tate’s book, which was published in 1993. The publication date of Dr. Tate’s fine work was after the forensic engineering studies of the bridge were well advanced. The connection between the ruined structures in the river and Structure 5 on the Grand Plaza changed the character of the bridge and expanded the focus of our engineering research to include the dramatic effect of the bridge structure on the Grand Plaza. A review of the digitized site map indicated that Structure 5 appeared to be in alignment with the bridge structures. This alignment enhanced the engineering hypothesis for the geometry of the bridge structure: a three-span suspension bridge once spanned the river and terminated its approach structure on an elevated esplanade that also served as the top platform for a grand stairway extending up from the riverfront. This exciting concept had to be proven by additional field investigation and computer-based bridge design applications in order to verify the altered
hypothesis. The research and investigation for the bridge structure had to be thoroughly researched and developed properly, or the archaeological community could not be convinced of the existence of the bridge.

  The archaeological maps were scanned and the geometry of the structures on the Grand Plaza was integrated into the comprehensive plan exactly as surveyed. The scanned site graphics were introduced into the digital analysis and the bridge geometry from field surveys. Then aerial photos were integrated with the historical site maps to develop a composite plan. Field survey measurements taken at the site were used to confirm the distance between the edge of the riverbanks and the center alignment of the bridge pier structures.

  This comprehensive computer site analysis indicated that the river was approximately 20 percent greater in width on the historical maps than was measured during the field surveys. The geometry of the river banks and pier structure locations in the river were digitally adjusted on the archaeological map of the site. This combination of historic mapping and digitally corrected data generated an accurate dimensional and geometrical image of the angular centerline of the bridge with the Grand Plaza.

  Introducing data from the aerial photographs, the angle of incidence between the centerline of the two bridge pier structures and the edge of the south riverbank was established from the aerial photographs. Using the known location of the south bridge pier as a fixed point, the angle of incidence between the bridge centerline and the river edge was introduced into the computer model in order to extrapolate the centerline onto the Grand Plaza.

  The resulting computer graphic indicated that the centerline of the bridge extended southward over the riverbank and intersected with the eastern end of Structure 5 on the Grand Plaza. It was quickly recognized that Structure 5 possessed the logical design configuration and artistic dignity to serve as the terminus of the bridge on the Grand Plaza. The centerline of the bridge aligning with the two pier structures and intersecting Structure 5 confirmed the discovery of a rare find in engineering history. The conclusions of Dr. Tate in her book were confirmed: Structure 5 was the bridge approach structure and served, along with the stairway, as the impressive gateway to Yaxchilan.

  With the planar locations of the bridge and its structures identified, it was important to verify the capabilities of the bridge to span the river at a safe elevation above the high water level during flooding. The topographical maps indicated that the top surface of Structure 5 is approximately 22 meters above the riverbank at low water level. Historical records indicated that the flood levels of the river have occurred at a height of 15 meters above the low water mark. The elevation of Structure 5 at 22 meters above the low water mark placed the top surface of Structure 5 at 7 meters above the high water mark. This geometric arrangement fulfilled another engineering requirement: flood safety. The key elements of the bridge, including the top of Structure 5, the causeway to the southern abutment, the surface of the suspended timber bridge decking, and the northern abutment, were placed well above normal seasonal flood levels.

  The discovery of the intersection of the bridge centerline with Structure 5 was an exciting development. The synthesis of the collected data and computer modeling developed a logical basis for the existence of this lost landmark of ancient engineering.

  Figure 10-7: Site map of Yaxchilan with bridge structures located. Author’s image.

  The 1994 Site Visit to Confirm the Bridge Structure

  Prior to finalizing the computer simulations and modeling efforts, a further field expedition was launched to verify, on the ground, the alignment of the bridge structures and the plaza structures through actual site observations and surveys. In April 1994, the ceremonial city of Yaxchilan was again visited to investigate and verify the geometrical relationships developed during the forensic engineering analysis and computer applications that reconstructed this unique bridge structure. Again there were surprises; the road to Yaxchilan included an unexpected adventure.

  During 1994, the Zapatista Army of National Liberation under the control of the mysterious Subcomandante Marcos declared war against the Mexican State. Dr. Nicholas Hellmuth and I were traveling to Yaxchilan, and we came prepared to cross the battle lines in Chiapas. We were shorthanded because of concern for the unstable political situation and the requirement for crossing the active battle lines in Chiapas on the way to the river and to Yaxchilan. We were working under the auspices of a permit issued by INAH and a letter of safe conduct issued by Theodoro Maus, the Consul General of Mexico in Atlanta and a personal friend. These official documents, I thought, should work. But to guarantee our safe passage through the lines, we also packed bottles of tequila and cartons of Marlboro cigarettes in our backpacks.

  The single road from Palenque to the town of Fonterra on the Usumacinta and our cuyuco to Yaxchilan had a series of roadblocks and checkpoints manned by the Mexican Army and the opposing Zapatista rebels. Passing through the Mexican Army checkpoints with their neat revetments was formal. They inspected our INAH papers and safe-conduct letter, and approved of our archaeological mission. They searched the car and then passed us through. The Zapatistas were much less formal. A single felled tree blocked the road, marking their lines. We did not see the first ski-masked sentinel until he stepped out of the bush and barked, “Who are you and where are you going?” Just as in the movie The Treasure of the Sierra Madre, they were not interested in our “stinking papers.” Once they found we were on an archaeological mission, they were actually quite friendly and really cheered up when we gave them our gifts: a carton of Marlboro cigarettes and a bottle of tequila. We were then given permission to pass on. I thought I would really impress them when I told them that Emilio Zapata and I shared the same birth date. Not so. They did not hear my qualifications that I was sure would make me an honorary Zapatista. Instead they were busy laughing with each other and happily sharing the carton of cigarettes. I don’t know about the tequila, but we continued on our way to the Usumacinta River and our awaiting cayuco.

  During this visit to Yaxchilan, the alignment of the centerline of the salient bridge components (the bridge piers, the river stairway, and the mysterious Structure 5) were observed, surveyed, photographed, videotaped, and mapped. The topographical survey and the field evidence clearly indicated that the mystery of Structure 5 was solved. The survey instruments showed that the centerline of the bridge intersected with the southeast part of Structure 5. The engineering hypothesis of the long-span suspension bridge at Yaxchilan was verified. The monumental platform of Structure 5, with its grand hieroglyphic stairway, was the terminus of the grand suspension bridge over the river as well as the Grand Stairway leading up from the riverfront. The confluence of the bridge and the stairway at the Plaza level verified the theory that Structure 5 was the grand entrance to the great city of Yaxchilan.

  Computer Simulation and Virtual Reconstruction of the Bridge

  Based on the confirmed data from the 1994 expedition, an updated computer simulation and a structural engineering analysis for the bridge were developed. The research and analysis confirmed that seventh century Maya engineers constructed a long-span, rope cable suspension bridge across the Usumacinta River. The rope-cable support system was supported from tall composite stone and cast-in-place concrete bridge towers and anchored by stone mechanisms at the north and south abutments. The rope cable suspension system was connected to a series of suspender ropes that supported the timber bridge-deck system.

  The geometry and design were integrated into computer graphics. The geometry of the structural towers and centerline dimensions of the towers are based on the measured field survey (Figure 10-8). The walkway height was established by the elevation of Structure 5. A vaulted Maya arch at the top of the bridge piers served as a three-dimensional structural support for the rope cable guide ways (Figure 10-9). The bridge pier and the vaulted arch were constructed of a stone exterior with a cast-in-place concrete interior. It was important that the rope cable guideways be connected into the mass of t
he concrete wall of the tower arch to optimize the stabilizing effect of the vaulted arch. Large forces were generated by the rope cable support system, and the supports required substantial resistance.

  Figure 10-8: Plan of bridge structure showing Grand Stairway and Causeway. Author’s image.

  Figure 10-9: Elevation of bridge tower pier showing lowest water level and overall dimensions. Author’s image.

  The rope cable suspension system assumed a catenary shape typical of cable-supported bridge systems (Figure 10-10). The center-to-center span between the bridge support piers in the river, based on field surveys, is 63 meters. A vertical dimension of 5 meters was selected for the sag in the rope cable system. This amount of sag was selected to carry out engineering calculations for the forces generated in the rope cable. The weight to be supported by the bridge cables was calculated using the maximum number of people assumed to be walking in a ceremonial procession while crossing the bridge, plus the dead load of the bridge deck. Beasts of burden did not exist in Mesoamerica, so rolling loads from carts were not included.

  Figure 10-10: Elevation of bridge structure with Yaxchilan Grand Plaza and river structures. Author’s image.

  The bridge deck was assumed to be 3 meters wide and made of wooden planks spanning between cross beams supported by suspender ropes connected to the cable support system. Using the known strength of hemp rope, calculations indicated that the rope cable system would require a bundle of 5-centimeter diameter ropes on each side of the bridge walkway. I commissioned an architectural rendering of the bridge (Figure 10-11) and a three-dimensional computer fly-through (Figure C-22).