Bolivia

In Bolivia, stone blocks were ground with sand so precisely that some believe aliens made them.

At a temple on Bolivia’s high plateau lie blocks of hard volcanic stone, cut so precisely that they fit together without mortar. They have inspired wild theories of unknown technology and visitors from space.

But some blocks were left unfinished, and they show how it was done. First the shape was pounded out with stone hammers. Then the surface was ground, slowly, with flat stones and sand.