Of these, only the Olmec civilization developed in a lowland tropical forest setting.
The Olmecs were the first inhabitants of the Americas to construct monumental architecture and to settle in towns and cities.
This is the only known example from outside the Olmec heartland.
All portray mature individuals with fleshy cheeks, flat noses, and slightly crossed eyes; their physical characteristics correspond to a type that is still common among the inhabitants of Tabasco and Veracruz. The boulders were brought from the Sierra de los Tuxtlas mountains of Veracruz.
Given that the extremely large slabs of stone used in their production were transported over large distances, requiring a great deal of human effort and resources, it is thought that the monuments represent portraits of powerful individual Olmec rulers.
The period of production of the colossal heads is therefore unknown, as is whether it spanned a century or a millennium.
All of the stone heads have been assigned to the Preclassic period of Mesoamerican chronology, generally to the Early Preclassic (1500–1000 BC), although the two Tres Zapotes heads and the La Cobata Head are attributed to the Middle Preclassic (1000–400 BC).
Each of the known examples has a distinctive headdress.
The heads were variously arranged in lines or groups at major Olmec centres, but the method and logistics used to transport the stone to these sites remain unclear.
Two thirds of Olmec monumental sculpture represents the human form, and the colossal heads fall within this major theme of Olmec art. However, the San Lorenzo heads were buried by 900 BC, indicating that their period of manufacture and use was earlier still.
The heads from Tres Zapotes had been moved from their original context before they were investigated by archaeologists and the heads from La Venta were found partially exposed on the modern ground surface.
The backs of the heads are often flat, as if the monuments were originally placed against a wall.