The Inca civilization originated in Peru and grew to cover over 2,500 miles across western South America by the 15th century, comprising around 12 million people. Ruled by a divine king called the Sapa Inca, the Inca built infrastructure like the 2,000 mile Royal Road and suspension bridges. They developed advanced agricultural techniques using terracing. The Inca had no written language but used knotted string records and a messenger system to efficiently govern their vast empire.