The Inca road system was the most extensive and highly advanced transportation system in pre-Columbian South America. The network was based on two north-south roads, with numerous branches. The best known portion of the road system is the Inca Trail to Machu Picchu.
The eastern route ran high in the puna and mountain valleys from Quito, Ecuador to Mendoza, Argentina. The western route followed the coastal plain except in coastal deserts where it hugged the foothills. More than 20 routes ran over the western mountains, while others traversed the eastern cordillera in the mountains and lowlands. Some of these roads reach heights of over 16,000 ft above sea level. The trails connected the regions of the Inca empire from the northern provincial capital in Quito, Ecuador past the modern city of Santiago, Chile in the south. The Inca road system linked together about 25,000 mi of roadway and provided access to over 1,200,000 sq mi of territory.
Situated between 1,600 to 2,600 ft above sea level, this monumental road, which could reach 66 ft in width, connected populated areas, administrative centers, agricultural and mining zones, as well as ceremonial centers and sacred spaces.
These roads provided easy, reliable, and quick routes for the Empire's civilian and military communications, personnel movement, and logistical support. The prime users were imperial soldiers, porters, and llama caravans, along with the nobility and individuals on official duty. Permission was required before others could walk along the roads, and tolls were charged at some bridges. Although the Inca roads varied greatly in scale, construction, and appearance, for the most part they varied between about 3.3 to 13 ft in width.
Much of the system was the result of the Incas claiming exclusive right over numerous traditional routes, some of which had been built centuries earlier. Many new sections were built or upgraded substantially: through Chile's Atacama desert, and along the western margin of Lake Titicaca, serve as two examples.
Information based on http://en.wikipedia.org/wiki/Inca_trail