"On the side of Saqsayhuayman that is less steep are three walls, one above the other. The most beautiful thing that can be seen among the buildings of that land are these walls, because they are of stones so large that no one who sees them would say that they have been placed there by human hands, for they are as large as chunks of mountains, and they have a height of thirty palms [twenty-one feet) and a length of as many more. These walls twist in such a way that if they are bombarded with cannons it is impossible to do so from directly in front, but only obliquely. The whole fortress was a warehouse of weapons, clubs, lances, bows, axes, shields, vests thickly padded with cotton, and other weapons of various sort gathered from every corner of the realm that was subject to the Inca lords."
PHOTOGRAPHER'S JOURNAL, "Cuzco," part 7: The siege of Cuzco was directed from Saqsayhuaman, high above the burning city. Its strategic location was critical for the noose that Manco was drawing around the Spanish forces. As Manco's armies closed in on the city, they pushed the Spanish toward the plaza beneath Saqsayhuaman. From above Manco launched punishing raids down the hillside which gave his forces the advantage of height.
So long as Manco remained in control of Saqsayhuayman, the foreigners were doomed.