The Inca Empire expanded greatly between 1438 and the 16th century to include parts of modern-day Ecuador, Peru, Bolivia, Argentina, Chile and Colombia. The Inca developed an advanced civilization with distinct social hierarchies, impressive architecture, sophisticated agricultural techniques, and a system of knotted strings called quipus for record keeping. Their capital was Cusco, and their official language was Quechua, with the sun god Inti at the center of their religion.