The Maya were one Mesoamerican culture that had strong ties to Teotihuacan. Maya’s architectural and mathematical contributions were significant. Flourishing from roughly 2000 BCE to 900 CE in what is now Mexico, Belize, Honduras, and Guatemala, the Maya perfected the calendar and written language the Olmec had begun. They devised a written mathematical system to record crop yields and the size of the population and to assist in trade. Surrounded by farms relying on primitive agriculture, they built the city-states of Copan, Tikal, and Chichen Itza along their major trade routes, as well as temples, statues of gods, pyramids, and astronomical observatories. However, because of poor soil and a drought that lasted nearly two centuries, their civilization declined by about 900 CE and they abandoned their large population centers.