The Inca Empire was the largest empire in pre-Columbian America. The Inca civilization arose sometimes in the early 13th century. It was a highly sophisticated society when the Spanish arrived. The last Inca stronghold was conquered in 1572. In the course of the conquest the Spanish destroyed most of the Inca’s quipus – talking knots – and with them the ability to read them, as well as most other aspects of the Inca culture like their sophisticated farming system. They used the population as slaves in the gold and silver mines where the average life span was about one year. Smallpox, typhus, diphtheria, measles, and influenza – epidemic diseases brought in by the Europeans – killed most of the people slavery didn’t.