Mesoamerican chronology  Mesoamerican chronology divides the history of prehispanic Mesoamerica into several periods: the Paleo-Indian (first human habitation – 3500 BCE), the Archaic (before 2600 BCE), the Preclassic or Formative (2500 BCE – 250 CE), the Classic (250–900 CE), and the Postclassic (900–1521 CE), Colonial (1521–1821), and Postcolonial (1821–present). The periodization of Mesoamerica by researchers is based on archaeological, ethnohistorical, and modern cultural anthropology research dating to the early twentieth century. Archeologists, ethnohistorians, historians, and cultural anthropologists continue to work to develop cultural histories of the region.  10,000–3500 BCE The Paleo-Indian (less frequently, Lithic) period or era is that which spans from the first signs of human presence in the region, to the establishment of agriculture and other practices (e.g. pottery, permanent settlements) and subsistence techniques characteristic of proto-civilizations. In Mesoamerica, the termination of this phase and its transition into the succeeding Archaic period may generally be reckoned at between 10,000 and 8000 BCE. This dating is approximate only and different timescales may be used between fields and sub-regions. Before 2600 BCE  During the Archaic Era agriculture was developed in the region and permanent villages were established. Late in this era, use of pottery and loom weaving became common, and class divisions began to appear. Many of the basic technologies of Mesoamerica in terms of stone-grinding, drilling, pottery etc. were established during this period.  2000 BCE – 250 CE  During the Preclassic Era, or Formative Period, large-scale ceremonial architecture, writing, cities, and states developed. Many of the distinctive elements of Mesoamerican civilization can be traced to this period, including the dominance of corn, the building of pyramids, human sacrifice, jaguar-worship, the complex calendar, and many of the gods. The Olmec civilization developed and flourished at such sites as La Venta and San Lorenzo Tenochtitlán, eventually succeeded by the Epi-Olmec culture between 300–250 BCE. The Zapotec civilization arose in the Valley of Oaxaca, the Teotihuacan civilization arose in the Valley of Mexico.