How The Incas Built Bridges Over Gorges

Inca rope bridges were simple suspension bridges over canyons and gorges and rivers (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. The bridges were an integral part on the Inca road system and are an example of Inca innovation in engineering. They were frequently used by Chasqui runners delivering messages throughout the Inca Empire.[1]
The Incas used natural fibres found within the local vegetation to build bridges. These fibres were woven together creating a strong enough rope and were reinforced with wood creating a cable floor. Each side was then attached to a pair of stone anchors on each side of the canyon with massive cables of woven grass linking these two pylons together. Adding to this construction, two additional cables acted as guardrails. The cables which supported the foot-path were reinforced with plaited branches. This multi-structure system made these bridges strong enough to even carry 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 death. An Inca author praised Spanish masonry bridges being built, as this made 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 Cuzco.