The Inca civilization originated in Peru in the 13th century and built a vast empire through military conquest. By the 15th century, the Inca Empire spanned much of western South America and was organized into four regions with Cuzco as its capital. The Incas had no written language but used knotted strings called quipus to record information. They developed advanced architecture, road systems, agriculture and other innovations without the use of wheels or iron. The Inca Empire was the largest in pre-Columbian America until its collapse following the Spanish conquest in the 16th century.