Machu Picchu, the Incan city built on a jagged mountain peak, is so remote that the Spanish conquistadors never found it. It’s difficult to get to, even today.

We’ve long wondered why the Inca built it there. New research suggests they chose the site because it’s on the intersection of fault lines.

That would seem like a terrible place to build any city! But the Inca had good reasons.

The faults would have fractured the rocks there, making it easier for the Inca to dig and build flat terraces on which they built their structures and farmed their crops.

The fractured rocks were also easier to shape into the precise blocks they used to build their earthquake-resistant architecture: thick, backward-sloping walls with small, trapezoidal windows.

The faults drained water away from the site in this area prone to flash floods. But they also carried water to it from higher mountain ranges, important because between floods, there was often little water.

In fact, scientists believe that’s how the Inca found the faults in the first place: by following water seeps and drainages in the valley farther up into the mountains, to the place the faults intersected.

We’ve come to realize that one reason for the Inca’s remarkable success in the difficult Andean environment was a keen understanding of its fault systems.

Perhaps it’s not surprising then, that Cusco and several of their other cities were also built near fracture zones.