This Preclassic-period archaeological culture of Mexico's tropical southern Gulf Coast, extant around 1200–500 BCE, is significant as the first Mesoamerican society to create stone monuments, a trait that for centuries set them apart from their contemporaries. An “archaeological culture” is defined by scholars on the basis of a distinctive complex of artifacts that occur within a restricted geographic region. The archaeological culture called “Olmec” was first distinguished by magnificent stone monuments found on Mexico's southern Gulf Coast within a limited area extending from the Tuxtla mountains of southern Veracruz approximately 160 kilometers (100 miles) east to the humid lowlands of western Tabasco. That area was a source of rubber production in pre-Hispanic times, and “Olmec” essentially means “people of the rubber country,” but that name was given by modern scholars; what the Preclassic peoples of that region called themselves will never be known. Although more than two dozen sites with monuments are known in the Olmec area, the majority of the carvings occur at just three large sites: La Venta, San Lorenzo, and Laguna de los Cerros. (See link to "principal sites of cities" to see where they are, or look at the map below.) This suggests that those sites were major Olmec political-religious centers. Numerous other sites, each with only a few monuments, may have been secondary centers. The majority of Olmec settlements were populated by rural farmers and are more difficult to discover because they lacked stone monuments.

La Venta was the first Olmec center to receive intensive excavations. The excavations there yielded impressive discoveries: tombs containing jadeite offerings, numerous caches of jadeite celts,

(jadeite celt)

and large buried mosaic “pavements” created from serpentine blocks.

The 1950s research provided the first radiocarbon dates from an Olmec site, c.800–400 BCE, and those helped to clarify the Olmec's position in Mesoamerican prehistory, but the discoveries contained scant information on the nature of Olmec society or of its antecedents.

Such data began to be provided by excavations carried out at San Lorenzo in the late 1960s to investigate the lifeways of the Olmec—domestic and public architecture, subsistence activities, and monument manufacture. This research placed the Olmec further back in time than previously imagined and included pre-Olmec levels. The easternmost Olmec center, La Venta, is situated on the humid, tropical coastal plains of Tabasco, adjacent to the Tonalá River and close to the rich marine resources of the coastal estuaries of the Gulf of Mexico. Although there is evidence of settlements in that area as early as 1700 BCE, La Venta seems to have flourished as a center particularly in the years c.900–500 BCE, in the latter half of Olmec prehistory. It therefore provides a view of Olmec developments at that time period. For example, La Venta's central area is notable for its tall earthen truncated platform mounds that extend in groups for over one-half mile. Incorporated near the north end of those platform groups is Mound C-1, a 30-meter (100-foot) tall earthen pyramid, one of the largest in Mexico at 700 BCE.

Those two forms of public architecture, as well as the tombs and jadeite offerings found during the early excavations, are mainly traits of the 900–500 BCE time period in the Olmec region.

More than eighty stone monuments have been discovered at La Venta, and most were situated in the plaza areas immediately to the north and south of the Mound C-1 pyramid. Four major classes of monuments were created by La Venta's artisans: colossal stone heads, massive tabletop thrones (also known as “altars”), large vertically erected stelae displaying bas-relief carvings, and three-dimensional statues. These monument classes are typical of the entire Olmec realm. A second common feature of monuments is that throughout the realm, almost all carvings were created from a particular type of basalt found in the Tuxtla Mountains, an area far distant from La Venta, San Lorenzo, and most other Olmec sites. Just how those multi-ton stones were moved across the heavily forested tropical riverine landscape of that region remains a matter of conjecture.

The center of San Lorenzo, 56 kilometers (35 miles) inland from the Gulf of Mexico, is situated atop a long hill-top plateau overlooking the vast floodplain of the Coatzacoalcos River Basin. The inhabitants of the hilltop artificially leveled and otherwise modified the hill's upper surface, during both pre-Olmec and Olmec times, to create a plateau area over 1000 meters long and up to 750 meters wide. San Lorenzo was at its zenith as an Olmec center from about 1150 to 900 BCE, and it therefore provides data on the initial period of Olmec prehistory. The platform mounds, pyramids, and clearly defined plaza areas found at La Venta are absent at San Lorenzo, and public architecture at that time may instead have been in the form of large houselike structures erected atop low platforms.

The research conducted at San Lorenzo has provided the best information on Olmec lifeways. The Olmec diet there included maize, beans, squash, fish, dogs, deer, rabbits, and iguanas. Domestic (house) structures varied in size and elaboration, from large structures built upon a raised clay platform to simple wattle-and-daub houses with tamped-earth floors.

An intriguing construction feature found at both San Lorenzo and La Venta is their subsurface network of stone water conduits. These were constructed using long rectangular blocks of basalt, each hollowed into a U shape and capped by a thin basalt cover stones to create a hollow “pipe.” The conduit stones were laid end to end over long distances, and the entire conduit system was then buried. Although they were once considered by researchers to be “drain lines,” new evidence indicates that these unusual conduit systems carried fresh water from local subsurface aquifers to various areas of the Olmec settlements. On occasion, special carvings were incorporated into the system. For example, San Lorenzo's Monument 9, a large stone basin sculpted in the form of a duck, was apparently placed at the end of a conduit system to receive the water that exited the system.

More than sixty monuments have been found at San Lorenzo. Those include ten colossal stone heads and two tabletop thrones. La Venta, in comparison, has five tabletop thrones but only four colossal heads. Stone stelae, common at La Venta, are rare at San Lorenzo, suggesting that stelae are a monument class that became important primarily after 900 BCE. The majority of San Lorenzo's colossal heads were displayed in linear arrangements in the southern area of the plateau, each sitting atop a specially prepared bentonite clay floor.

Two colossal stone heads occur at Tres Zapotes, a secondary center near the western edge of the Olmec realm, and therefore the site has frequently been mischaracterized as a major Olmec center. Although more than two dozen monuments occur there, only the colossal heads and perhaps four other carvings can be considered Olmec; the large remainder are Late Preclassic (post-Olmec). However, Tres Zapotes is an extremely significant site precisely because it reveals a clear evolution out of the Olmec monument tradition. Within the Olmec realm, nearly two hundred monuments are known. Many of them seem to depict Olmec rulers—their stone portraits, commemorating them in life or remembering them in death. Motifs displayed in their head coverings may have been identification symbols. However, a large percentage of the carvings exhibit purposeful mutilation: heads and arms have been broken from the statues; some personages shown in bas-relief carvings have had their faces “erased”; and large fragments have been broken from some tabletop thrones. Only the colossal heads were spared. Scholars originally attributed such damage to non-Olmec invaders or to an internal revolution in the Olmec realm, but most researchers now believe that the mutilation was carried out by the Olmec themselves for ritual purposes, perhaps at the death of the personage depicted. However, some breakage may have served more mundane purposes; recent excavations at San Lorenzo have revealed an area of monument “recycling,” where carvings were reworked into new images. Furthermore, evidence indicates that two rectangular table top thrones at San Lorenzo were later resculpted into colossal stone heads, an indication that the breakage of large pieces from such thrones may merely have been the first step in rounding the rectangular altar into the ovoid form for a colossal head.

Two forms of evidence suggest the Olmec might have played a version of Mesoamerica's ballgame. Ballgames have great antiquity throughout the Americas. Some, but not all, of the Mesoamerican variations of the game were played in actual ballcourts defined by long parallel mound constructions. Parallel mound structures at La Venta and fragments of two small mounds exposed in the Palangana-phase (700–500 BCE) strata at San Lorenzo may be the remnants of Olmec ball-courts. Far more convincing evidence comes from the site of El Manatí, a freshwater spring at the base of a small hill in the Coatzacoalcos River floodplain ten kilometers (six miles) east of San Lorenzo. There, a chance discovery of preserved wooden artifacts in the spring's mud led to several years of archaeological research, during which an amazing quantity of wooden Olmec artifacts were recovered, including “baby-face” heads (busts) and staffs. The Olmec had apparently placed these objects in the spring as ritual offerings. Surprisingly, among the other objects discovered were more than a dozen rubber balls, the oldest known in Mesoamerica.

In the initial stages of Olmec archaeology, when knowledge was restricted to the data obtained from La Venta, the origins of the Olmec seemed puzzling. Scholars hypothesized migrations to the Gulf Coast from other regions of Mesoamerica where Olmec-looking artifacts occur, and a few suggested Chinese or African affiliations. Most of those notions faded quickly when the San Lorenzo excavations unearthed a lengthy pre-Olmec archaeological record which demonstrates that the Olmec evolved there. They were a society indigenous to that area, and they probably spoke a language related to modern Mixe-Zoque. Their achievements were theirs, not borrowed from others near or far.

The focus of Olmec research has been on the early period of Olmec prehistory and on their lifeways. Therefore, almost nothing is known of their “demise,” but because Olmec is an archaeological culture defined by certain artifacts, the “end” of Olmec is merely the disappearance of that artifact complex. There are no data to indicate whether the decline of the major Olmec centers and the disappearance of the defining artifact complex was rapid or gradual. The Late Preclassic monuments at Tres Zapotes strongly suggest that over time, the Olmec simply evolved out of the traits by which they were originally defined. Whatever the case, their legacy is most clearly found in the rulership monuments of the Classic period Maya.