The Mayan civilization dates back to 2000 B.C., and extended through what is now southern Mexico, Guatemala, Belize, El Salvador, and parts of Honduras. During the civilization's peak, from A.D. 300 to 900, the Mayans not only built towering temples and pyramids but also created elaborate astronomical maps and calendars and sophisticated mathematical systems. The civilization went into decline after 900, and its once-teeming cities were soon abandoned. Historians dispute why this happened; some say the Mayans were decimated by a 200-year drought, while others say they brought on their own downfall through over-farming. About 10 million descendants of the Mayans still live in Central America.