History of the world
Whether in prehistoric or historic times, people always needed to be near reliable sources of potable water. Settlements developed on river banks as early as 3000 BCE in Mesopotamia, on the banks of Egypt's Nile River, in the Indus River valley, and along China's rivers. As farming developed, grain agriculture became more sophisticated and prompted a division of labour to store food between growing seasons. Labour divisions led to the rise of a leisured upper class and the development of cities, which provided the foundation for civilization. The growing complexity of human societies necessitated systems of accounting and writing.
Chiapas
Recent excavations in the Soconusco region of the state indicate that the oldest civilization to appear in what is now modern Chiapas is that of the Mokaya, which were cultivating corn and living in houses as early as 1500 BCE, making them one of the oldest in Mesoamerica. There is speculation that these were the forefathers of the Olmec, migrating across the Grijalva Valley and onto the coastal plain of the Gulf of Mexico to the north, which was Olmec territory. One of these people's ancient cities is now the archeological site of Chiapa de Corzo, in which was found the oldest calendar known on a piece of ceramic with a date of 36 BCE. This is three hundred years before the Mayans developed their calendar. The descendants of Mokaya are the Mixe-Zoque.