The Andes experience two distinct seasons: dry and rainy. The rainy season lasts from November to April.

This steep slope near Machu Picchu shows just how critical it was for the Inka to control soil erosion caused by heavy rainfall. Certain regions from the Andes, particularly the upper Amazon, can receive up to 76 inches or 193 centimeters of water a year. Most of that rain falls during the rainy season from November to April. In comparison, Washington, D.C., receives around 39 inches or 99 centimeters per year.

The deep vertical grooves on the side of this mountain are marks of soil erosion caused by heavy rainfall. The Inka built upon the experience of their ancestors and the local populations to mitigate soil erosion. They also developed new techniques to manage water and to ensure the long-term survival of their building projects.

Every stretch of the Inka Road was built in response to the challenges of the surrounding environment. The goal was to make roads that would last. This drainage culvert was built beneath an Inka road near Machu Picchu. It also served as an underpass through which people could travel.

Water management engineering is a hidden marvel of sites like Machu Picchu. Without careful planning, the site’s most iconic structures, such as the temple of the sun or the guardhouse seen in this picture, would have not survived.

Much of the site’s most complex engineering work lies underground. By building terraces on steep hillsides, the Inka increased the amount of agricultural land. Through construction of terraces and colcas, or storehouses, and the careful management of resources, the Inka were able to feed their massive empire.

Terraces were engineered with water in mind. Water was redirected to decrease its force and prevent soil erosion. Underground drainage systems captured the heavy rainfall, channeling it for irrigation and other uses.