The Inca road system was the most extensive and advanced transportation system in pre-Columbian South America. It was about 39,900 kilometres (24,800 mi) long.[1]:242 The construction of the roads required a large expenditure of time and effort.[2]:634 The network was based on two north-south roads with numerous branches.[3] The best known portion of the road system is the Inca Trail to Machu Picchu. Part of the road network was built by cultures that precede the Inca Empire, notably the Wari culture.