Huinchiri and Keshwa Chaca Rope Bridge
Inca rope bridges were simple suspension bridges over canyons and gorges (pongos) to provide access for the Inca Empire. Bridges of this type were suitable for use since the Inca people did not use wheeled transport -- traffic was limited to pedestrians and livestock. These bridges were an integral part on the Inca road system and are an example of Inca innovation in engineering. The bridges were frequently used by Chasqui runners delivering messages throughout the Inca Empire.
The construction of these bridges amounted to a pair of stone anchors on each side of the canyon with massive cables of woven grass linking the two pylons together. Adding to this construction, two additional cables acted as guardrails. The cables which supported the footpath were reinforced with pleated branches. This multi-structure system made these bridges strong enough to carry even the Spaniards while riding horses after they arrived. However, these massive bridges were so heavy that they tended to sag in the middle, and this caused them to sway in strong winds.
Part of the bridge's strength and reliability came from the fact that each cable was replaced every year by local villagers as part of their mita public service or obligation. In some instances, these local peasants had the sole task of maintaining and repairing these bridges so that the Inca highways or road systems could continue to function.
The repair of these bridges was dangerous, to the degree that those performing repairs often met with death. One Inca author write of his praise for Spanish masonry bridges being built, as this made for the need to repair the rope bridges moot.
The greatest bridges of this kind resided in the Apurimac Canyon along the main road north from Cusco.
The Keshwa Chaca, believed to be the last remaining Inca rope bridge, spans the Apurimac River near Huinchiri, Peru, in the Province of Canas. After a full year of use and exposure to the elements, the grass-rope bridge sags and must be replaced for safety. Even though there is a modern bridge nearby, the residents of the region keep the ancient tradition and skills alive by renewing the bridge annually every June. Several family groups have each prepared a number of grass-ropes to be formed into cables at the site, while others have prepared mats for decking. The reconstruction is a communal effort. In ancient times, the effort would have been a form of tax, with participants coerced to perform the rebuilding; nowadays the builders have indicated that effort is performed to honor their ancestors and the Pachamama (Earth Mother).
Information based on http://en.wikipedia.org/wiki/Inca_rope_bridge