Machu Picchu was built in the middle of the 15th century at the command of Pachacutec, ninth ruler of the Tahuantinsuyo and the one responsible for expanding it into what we call the Incan Empire. He was just twenty years old when he ascended the throne of his father, Viracocha, after he led the Incan armies in their defeat of the warlike Chancas. Wearing a colorful headdress, Pachacutec began his long reign that transformed the Andean world and built Cusco into the amazing city that left the Spanish Conquistadores stupefied. Seen in isolation from Europe or North America, it seems to be a marvelous anomaly, a city built on top of a mountain in a remote cloud forest, for unknown and possibly mysterious reasons. To accomplish this amazing feat, the builders had to remove massive quantities of stone and dirt and to construct enormous terraces, canals, foundations that were several meters deep, and monolithic walls of remarkable polished stones. It is believed that the city may have been used as a hiding place when the Spanish invaded, and despite the efforts made to locate it, Machu Picchu was never discovered by the Spaniards. Still, it is believed that the reason the city fell was due to the smallpox brought over by the Spanish, and that in trade with Cusco, the disease was transmitted. Less than a hundred years after being built it was abandoned.