Tiahuanacu is interesting because it is possible that the elaborate character of its symbolic sculpture may throw glimmerings of light on remote history; but Sacsahuaman, the fortress overlooking the city of Cuzco, is, without comparison, the grandest monument of an ancient civilization in the New World. Like the Pyramids and the Coliseum, it is imperishable. It consists of a fortified work 600 yards in length, built of gigantic stones, in three lines, forming walls supporting terraces and parapets arranged in salient and retiring angles. This work defends the only assailable side of a position which is impregnable, owing to the steepness of the ascent in all other directions. The outer wall averages a height of 26 feet. Then there is a terrace 16 yards across, whence the second wall rises to 18 feet. The second terrace is six yards across, and the third wall averages a height of 12 feet. The total height of the fortification is 56 feet. The stones are of blue limestone, of enormous size and irregular in shape, but fitted into each other with rare precision. One of the stones is 27 feet high by 14, and stones 15 feet high by 12 are common throughout the work. At Ollantay-tampu the ruins are of various styles, but the later works are raised on ancient cyclopean foundations.[1151] There are six porphyry slabs 12 feet high by 6 or 7; stone beams 15 and 20 feet long; stairs and recesses hewn out of the solid rock. Here, as at Tiahuanacu, there were, according to Cieza de Leon,[1152] men and animals carved on the stones, but they have disappeared. The same style of architecture, though only in fragments, is met with further north. East of the river Apurimac, and not far from the town of Abancay, there are three groups of ancient monuments in a deep valley surrounded by lofty spurs of the Andes. There is a great cyclopean wall, a series of seats or thrones of various forms hewn out of the solid stone, and a huge block carved on five sides, called the _Rumi-huasi_. The northern face of this monolith is cut into the form of a staircase; on the east there are two enormous seats separated by thick partitions, and on the south there is a sort of lookout place, with a seat. Collecting channels traverse the block, and join trenches or grooves leading to two deep excavations on the western side. On this western side there is also a series of steps, apparently for the fall of a cascade of water connected with the sacrificial rites. Molina gives a curious account of the water sacrifices of the Incas.[1153] The _Rumi-huasi_ seems to have been the centre of a great sanctuary, and to have been used as an altar. Its surface is carved with animals amidst a labyrinth of cavities and partition ridges. Its length is 20 feet by 14 broad, and 12 feet high. Here we have, no doubt, a sacrificial altar of the ancient people, on which the blood of animals and libations of _chicha_ flowed in torrents.[1154]