Small villages in River Valley Civilizations often grew into larger cities, and those cities became important centers of government, trade, and religion. Urban areas saw the development of specialization of jobs, such as scribes or merchants; social levels, such as elites and slaves; and gender roles, such as expectations that men would usually be government leaders and members of the military and women would usually engage in domestic functions like cooking, sewing, and child-rearing. Counting and writing systems began in cities as a means of keeping records of stored food and other goods. One of the first writing systems was cuneiform from Mesopotamia. Religious temples like Ziggurats in Mesopotamia are examples of monumental architecture that developed in early cities. Some examples of early cities in Eurasia are Sumer in Mesopotamia, Catal Huyuk in Turkey, and Mohenjo Daro and Harappa in South Asia's Indus River Valley. In the Americas, the Olmec civilization developed cities in Mesoamerica by 1600 BCE, and the Chavin civilization, along the cost of modern-day Peru, built urban centers by 900 BCE.