By the early 1500s CE, the Incas controlled a huge, well-organized territory limited mostly to the Andes Mountains. They certainly chose to build their empire in what might appear to be an unlikely place. The Andes consist of impassable ravines and towering peaks. Even the air in much of the range is nearly unbreathable—it's very "thin," thanks to the high elevation.
However, the Incas came up with some clever adaptations and innovations for life in the Andes. For starters, the Incas took advantage of foods that grow well in the mountains. They terraced mountainsides in order to cultivate native crops such as the potato. This nutrient-rich plant grows well at high elevations and can feed a large population. Additionally, in the mountains, livestock had to be kept small in order to deal with the lack of flat ground. The guinea pig, also native to the region, was a popular source of protein in the Andes (and still is today). This small rodent can be raised in small spaces built into the slopes of the hillsides.
Communication across a large mountainous empire may have been one of the Incas' greatest challenges. To deal with this, they built a system of roads, bridges, and rest houses to accommodate a system of relay runners who could quickly pass messages across a 2,500-mile-long territory. In all, about 15,000 miles of roads crisscrossed the territory of the Incas.
Mountains also serve as a natural form of defense. They protected the Incas from invading armies, who could not move quickly or efficiently across narrow mountain passes. This gave the Incan military time to mobilize an effective defense, which often included scuttling bridges or triggering avalanches to block the path of would-be invaders.