Inca Bridge
Inca Bridge. Photo (cc) Rutahsa Adventures.

When I wrote the Stonehenge module for the Integrated Sciences course I was reminded of a presentation I’d seen while taking my MPhil, but I couldn’t remember the speaker’s name. It’s John Ochsendorf, as I’ve found out after reading this New York Times story How the Inca Leapt Canyons. Ochsendorf’s work is an example of something where interdisciplinarity is a positive thing rather than a buzzword. In this case his research started at undergraduate level when he looked at Inca bridges.

Bridges are a pretty important part of the Inca road network because so much of the landscape in the Andes is vertical. The Inca bridges were therefore reliable, but to a European eye they were very strange, because the bridges were not built of stone or wood. Instead these were inspired by the first little pig. These were bridges built of grass.

It wasn’t even special grass. This was just stuff picked up lying around the hills, yet the bridges were strong enough to bear Spanish horses and cannon. So how do you get grass make a bridge strong enough to march an army across?

The answer is in the fibres and how they are intertwined. Pre-columbian South America was known for its gold, but the treasures that are smuggled out of Peru these days are usually woven fabrics. The Inca and other South American cultures were often master weavers, capable of weaving much finer cloth than we do today. Just at they wove magnificent textiles, so too they wove grass into strings, the strings into cords, the cords into ropes and the ropes into cables. The weaving worked with the strengths of the fibres to avoid awkward unravelling when someone was halfway across the bridge and the weaving massively multiplied the carrying capacity of the individual grass stems.

This is one of those bits of research which has potential across archaeology. In my case I was interested in how the stones were moved to Stonehenge as an engineering question. What I found is that there are some studies on ancient engineering, but they’ve made little impact on the major syntheses. The English Heritage Stonehenge books were showing utterly inadequate diagrams for lifting the stones with levers, and for most books rope was simply assumed to have existed.

It’s a safe assumption we know rope existed from impressions on Neolithic pots. Corded ware is named after impressions from cords wrapped around the pot before it was fired. Analysis shows that hemp was used for rope, but I’m less aware of work that has seriously tested the stress and strain of such ropes. Work like that is basic Physics but would give us an idea of what strengths ropes were being made for and may give us ideas of what capabilities Neolithic people had in shaping their environments. The materials used could be tested for strength. Were Neolithic people make optimal decisions for which rope they used, or could there be properties other than strength that they looked for in a rope?

For Neolithic you could read almost any other prehistoric or early historic culture. Similar opportunities must be there for people with a basic grasp of geology, biology or many other sciences. The biggest steps would be having the imagination to see where is a problem that’s been overlooked and then persuading archaeologists or historians that some assumptions they’ve been making could be unfounded. That’s what makes Ochsendorf’s work interesting the physics are tied to the social questions.