At its height in the 14th century, the Inca ruled an Empire of 12 million people, in an area that encompasses six modern South American nations. Archaeologist Noah Corcoran-Tadd describes a ceremonial network based on the sun that allowed the Incan government to monitor its vast expanse. Using history records and GPS mapping, Corcoran-Tadd discovered sacred markers, called huacas, which formed a network defining the wider sacred world within the Empire. The huacas converge on the Temple of the Sun in Cuzco, the center of the Empire.