How did geography influence how the Inca road system and Machu Picchu were built?

The Inca road system formed a network known as the royal highway or qhapaq ñan, which became an invaluable part of the Inca empire, not only facilitating the movement of armies, people, and goods but also providing an important physical symbol of imperial control. Across plains, deserts, and mountains, the network connected settlements and administrative centres. Well-built and lasting, many roads included bridges, causeways, stairways, also had small stations (chaskiwasi) and sometimes larger, more luxurious complexes (tambos) dotted along every 20 km or so, where travellers could spend the night and refresh.