The Incas Planned Macchu Picchu so that it could function independently of the outside world; people could live there without ever having to leave.
The southern slope was adapted for agriculture, with terraces cut into the mountainside that could be filled with earth brought up from the fertile Urubamba Valley.
These terraces, called “andenes” where retained by low walls. This let them be irrigated artificially without the soil washing away. The water was brought down to the terrace fields from the higher mountains by means of an ingenious network of canals and channels. This system of irrigations still functions today !