Sacsayhuamán
The account
Stones of more than a hundred tons fitted so precisely that not even a blade slips between them: a lost technique, softened rock or outside help.
What investigators found
An Inca construction from the 15th century, under the emperor Pachacútec. The stones were shaped and fitted one by one, without mortar, in a design that withstands earthquakes.
The story
On the hills above Cusco, the ancient capital of the Incas, rise the zigzag walls of Sacsayhuamán. Some stones exceed 100 tons and lock into one another with irregular corners, without any mortar, so tightly that they still impress engineers today.
Legends speak of a technique for softening stone, or of builders who came before the Incas. Archaeologists credit the work to the Inca Empire, beginning with the reign of Pachacútec in the 15th century. In 1536, it was the site of a decisive battle between Manco Inca's forces and the Spanish, who later used some of the stones to build colonial Cusco. What remains is precisely what was too big to haul away.