The massive fortified complex of Sacsayhuaman is the most significant ruin in Cusco, and is close enough to the historic center that you can walk there. Many tourists stop to see it on the way to Pisac. Sacsayhuaman is thought to have both military and religious significance. Cusco was designed in the shape of a puma, with Sacsayhuaman as the head. Three ramparts of zigzagging defense walls extend for almost 300 meters, forming the teeth of the puma.

The fascination of this ruin is not just its staggering size, but the size of the stones from which it was built, and the complexity of the stone work. Consider that what you see here is only about 20% of the original mass – until it was protected in the 1930s, blocks from Sacsayhuaman were being hauled away to use for construction in Cusco. Most of the largest stones, which were more difficult to move, were left at the site, and form the basic structure. Some of these stones measure more than eight meters high and weigh 361 tons. Despite the massive size of these stones and their often irregular shapes, they are fitted together so perfectly that modern engineers wonder at how the Incas managed such a feat.