The buildings are thought to have been planned and built under the supervision of professional Inca architects. Most of the structures are built of granite blocks cut with bronze or stone tools, and smoothed with sand. The blocks fit together perfectly without mortar, although none of the blocks are the same size and have many faces; some have as many as 30 corners.The joints are so tight that even the thinnest of knife blades can't be forced between the stones. Another unique thing about Machu Picchu is the integration of the architecture into the landscape. Existing stone formations were used in the construction of structures, sculptures are carved into the rock, water flows through cisterns and stone channels, and temples hang on steep precipices.