Though the Inca refused to admit it, much of their highway network and organizational know-how was based on the Huari Empire, which spread across Peru like a wildfire A.D. 500–1000.

An example of Huari engineering is Rumicolca, a huge aqueduct that sits on a valley pass on the side of the highway about 32 kilometers from Cusco. The Inca altered the construction, added a few stones, and converted it into a giant gateway to Cusco, though the remains of the old water channels can still be seen.

Nearby is Pikillacta (6 a.m.–6 p.m., US$2), the largest provincial outpost ever built by the Ayacucho-based Huari. This curious walled compound, with nearly 47 hectares (116 acres) of repetitive two-story square buildings, sprawls across the rolling grasslands with little regard to topography.

The floors and walls, which are made of mud and stacked stone, were plastered with white gypsum and must have gleamed in the sun. But the Inca so thoroughly erased evidence of the Huari that little about their empire is known today.

For many years Pikillacta was thought to be a huge granary, like the Inca site of Raqchi. But excavations have revealed evidence of a large population that left behind refuse layers as deep as three meters. Part of the city caught fire between A.D. 850 and 900, and the Huari withdrew from the city around the same time, bricking up the doors as they went.

Whether they abandoned the city because of the fire, or burnt it as they left, is unclear. Some historical information is available at the new museum at the entrance. In the valley below is Lago Sucre and, even farther on, Lago Huacarpay. On the far shores of this lake are the ruins of Inca Huáscar’s summer palace, much of which continues to be enjoyed today by locals as the Centro Recreacional Urpicanca, the local country club.

From the shoulder of the highway, it is possible to see ceremonial staircases the Inca built into the landscape above the lake.