Most of the roughly 150 buildings in Machu Picchu were built of granite so their ruins look like part of the mountains. The Inca made regular blocks of granite fit so tightly together (without mortar) that there are areas where a knife cannot fit between the stones.
Many buildings had trapezoidal doors and thatched roofs. They used irrigation to grow corn and potatoes. Smallpox devastated the Machu Picchu before the conqueror of the Inca, the Spaniard Francisco Pizarro, arrived. Yale archaeologist Hiram Bingham discovered the ruins of the city in 1911.
Sources: Archaeology Guide - Machu Picchu
[formerly at < www.mnsu.edu/emuseum/prehistory/latinamerica/south/sites/machu_picchu.html> Machu Pichu]
Sacred Site's Machu Picchu
Machu Picchu - Wikipedia