The Patagonian system was a network of mirrors, mirrored spheres held up high at road junctions and in villages. Looking into a mirror, you can see another mirror. Each mirror is curved, so if you look close in the reflection you can see another mirror reflected, and another, and another, and so on. Using a telescope you can see all the way, bouncing off mirrors all the way. It’s the reverse of optic fibre cables, I suppose, in that you receive light instead of sending it.
This is the 1500s, and we can guess the system was going for some hundred years, which makes it contemporary with Galileo’s use of the telescope, I guess, and volcanic glass is abundant in Patagonia.
What I like especially is the consequences of such a network, because it means basically they didn’t need to travel. They didn’t need double-entry book-keeping for efficient commerce, like the Italians invented around the same time, because every transaction could be witnessed directly by both parties, since every mirror was – in theory – visible from every other mirror.