This is an interesting piece from the MIT's online newspaper about Inca suspension bridges. Constructed from fibers from cotton, grasses, and saplings, and llama and alpaca wool, these precarious-looking suspension bridges stretched to cross deep river canyons and achieved longer spans than any European masonry bridges at the time. The Inca were the only ancient American civilization to develop suspension bridges (although there is some tenuous question about whether the Maya used a suspension bridge across the Usumacinta at Yaxchilan), and they played a vital part in the road system that linked the vast Inca Empire.

Inca Leapt Canyons With Fiber Bridges