Answer :

The city, called Tiahuanaco, was built by a people who lived in the region before the Incas came to rule there. But who the builders of Tiahuanaco were, and why the city fell into ruin, no one knows for sure. The Indians in the region claimed that Tiahuanaco was built by the gods and is the oldest city on earth

Answer: D

Nobody knows why they disappeared :|8+<