Tlatilco culture is a culture that flourished in the Valley of Mexico between the years 1250 BCE and 800 BCE, during the Mesoamerican Early Formative period. Tlatilco, Tlapacoya, and are the major Tlatilco culture sites. Tlatilco culture shows a marked increase in specialization over earlier cultures, including more complex settlement patterns, specialized occupations, and stratified social structures. In particular, the development of the chiefdom centers at Tlatilco and Tlapacoya is a defining characteristic of Tlatilco culture.