various reasons, such as tracking the sun's movement. The oldest such circle
known to scientists can be found at Nabta Playa in Egypt. At around 7,000 years
old, this circle predates England's Stonehenge probably the world's best-known
prehistoric stone circle by more than 1,000 years. Nabta Playa's climate is
extremely dry today, but this was not always the case. ( 26 ), heavy