Horizon markers
Once ceramics had been adopted in Mesoamerica, techniques of manufacture and styles of shape and decoration tended to spread rapidly and widely across many cultural frontiers. These rapid diffusions, called horizons, enable archaeologists to link different cultures on the same time level. Good horizon markers for the Early Formative are colour zones of red pigment set off by incised lines; complex methods of rocker stamping (a mode of impressing the wet clay with the edge of a stick or shell); the tecomate, or globular, neckless jar; and Olmec excised pottery. The beginning of the Middle Formative over much of Mesoamerica is marked by the diffusion of a very hard, white pottery, decorated with incised lines, and by solid pottery figurines with large, staring eyes formed by a punch. The people who replaced and probably overthrew the Olmec of San Lorenzo about 900 bce had such pottery and figurines, the ultimate origins of which are still a puzzle.
During the Middle Formative, cultural regionalism increased, although the Olmec presence can be widely detected. The transition to fully settled life had taken place everywhere, and burgeoning populations occupied hamlets, villages, and perhaps even small towns throughout Mesoamerica, both highland and lowland.