With their magnificent architecture and sophisticated knowledge of astronomy and mathematics, the Maya boasted one of the great cultures of the ancient world. Although they had not discovered the wheel and were without metal tools, the Maya constructed massive pyramids, temples and monuments of hewn stone both in large cities and in smaller ceremonial centers throughout the lowlands of the Yucatán Peninsula, which covers parts of what are now southern Mexico and Guatemala and essentially all of Belize. From celestial observatories, such as the one at Chichén Itzá, they tracked the progress of Venus and developed a calendar based on a solar year of 365 days. They created their own system of mathematics, using a base number of 20 with a concept of zero. And they developed a hieroglyphic scheme for writing, one that used hundreds of elaborate signs. The demise of Maya civilization (which archaeologists call “the terminal Classic collapse”) has been one of the great anthropological mysteries of modern times. What could have happened?