The mountain fortress of Machu Picchu, Peru. Initially, it was believed that the various types of masonry found in Cuzco, Machu Picchu and other Inca structures dated from different periods. Today, it is thought that both the walls constructed from interlocking megalithic blocks and those made from smooth, uniformly sized stones, as well as the mortar-bonded fieldstone technique were all employed by the same master builders from the period after 1440, depending on their intended purpose: the megalithic construction method for retaining walls, smooth, evenly rounded ashlars for representative buildings, and mortar-bonded rubble stone walls – alongside adobe bricks – for functional buildings. In Machu Picchu, however, various elements, such as the oval Torreón, suggest that construction continued here even into the colonial period. Inca architecture otherwise features only rectangular or trapezoidal shapes, and vertical arches are completely absent, which, for example, imposed certain limitations on the construction of gates. - Book: Picture 125 - Peru - 1969