Why Were They Built?: Six Man-Made Wonders of the World

Monarchs die, dynasties crumble, and borders between states are redrawn.

Six iconic monuments, however, have remained firmly in place through centuries of wars and natural disasters.

Although the empires that created them vanished long ago, these structures are enduring testaments to wealth, power, and glory.

Excerpt:
In Peru, Machu Picchu is built between two fault lines. These are breaks in the earth's crust where plates of rock move against each other. When there is an earthquake the stones of Machu Picchu dance, or bounce, before settling back into place. Therefore, it has been safe from destruction for hundreds of years. This site was built by the Incas in the 15th century.