But first came the boom years, roughly A.D. 300 to 660. At the beginning of the so-called Classic Maya period, some 60 Maya cities—each home to between 60,000 and 70,000 people—sprang up across much of modern-day Guatemala, Belize, and Mexico's Yucatán Peninsula. (Explore an interactive map of key Maya sites.)

Surrounded by pyramids, plazas, ball courts, and government buildings, the urban Maya discussed philosophy, developed an accurate solar-year calendar, and relished a thick, bitter beverage made from cacao beans: the world's first hot chocolate.

Farmers, too, were riding high, turning hillsides into terraced fields to feed the burgeoning population.

Then came the bust, a decline that lasted at least two centuries. By 1100 the residents of once thriving Maya