Sacsayhuaman - At the top of the hill is the foundation of what were once towers. The main tower was in the middle and had a circular shape. There are three concentric rings that were the foundations of its three stories or levels; its original height is unknown but it must have been important because it dominated the whole city. This tower's central portion was used as an abundant water reservoir for supplying the complex; the water was harnessed from springs in the higher part of the northern mountains where there are also several reservoirs. Between the concentric rings there are foundations of 12 small transversal walls that served in order to protect the building from the enormous pressure of water stored up in the middle.