1High in the Andes mountains of Peru sits the lost city of Machu Picchu.
2The Inca built it in the fifteenth century without wheels or iron tools.
3Its stone walls fit together so tightly that a knife cannot slip between them.
4The city sits on a narrow green ridge between two sharp mountain peaks.
5Hundreds of stone terraces kept the hillside from washing away in heavy rain.
6Priests watched the sun through special windows to mark the changing seasons.
7When the Spanish arrived, the city was abandoned and slowly forgotten by the world.
8Thick jungle hid the mysterious ruins from outsiders for nearly four hundred years.
9An American explorer named Hiram Bingham brought it to international attention in nineteen eleven.
10Today it is one of the most visited historical sites in South America.
11Officials now carefully limit the number of daily tourists to protect the fragile stones.