Puma Punku
The account
Stone blocks with straight cuts, interior angles and holes so precise that they look like machine-made parts.
What investigators found
The work of the Tiwanaku culture, which mastered stonework in sandstone and andesite and used metal clamps between the blocks. The precision is impressive, but it does not require modern technology.
The story
Near Lake Titicaca, in Bolivia, almost 4,000 meters above sea level, lie the ruins of Tiwanaku, capital of a great Andean civilization. Inside it is Puma Punku, "the gate of the puma," built around 500 to 600 AD.
What stands out are the blocks scattered across the ground: smooth faces, right interior angles, aligned channels and holes. Some of them, the "H blocks," are almost identical to one another. The largest sandstone slab weighs more than a hundred tons. For supporters of the ancient astronaut theory, only modern machines could make cuts like these.
Archaeologists explain that the Tiwanaku mastered stonework with hard tools, abrasives and measuring templates, and held the blocks together with metal clamps poured while still molten. The precision is real and impressive. The only question is just how talented those engineers were.