Aerial remote sensing reveals details of an ancient Olmec site in Mexico

(CNN) – Aerial remote sensing of a wide region of Mexico has revealed hundreds of ancient Mesoamerican ceremonial centers, including a large one at an important site of ancient Olmec culture, known for its colossal stone heads.

The remote sensing method, called lidar, has made it possible to locate 478 ceremonial centers in areas where the ancient Olmec and Mayan cultures lived, dating back to the period of 1100-400 BC, the researchers reported Monday. The study is the largest conducted in ancient Mesoamerica and covers the entire state of Tabasco, southern Veracruz, and parts of Chiapas, Campeche, and Oaxaca.

The lidar, short for Light Detection and Ranging, uses a pulsed laser and other data obtained by flying over a location to generate three-dimensional information about the shape of surface features. It penetrates vegetation and locates structures that could not otherwise be seen from the air or the ground.

A large ceremonial center was detected in the primitive Olmec site of San Lorenzo, located in Veracruz, in the lowlands near the Gulf of Mexico, and which had its heyday between approximately 1400 and 1000 BC. The Olmecs represented the oldest known Mesoamerican civilization and are believed to have influenced later cultures, including the Maya.

University of Arizona archaeologist Takeshi Inomata, who led the study published in the journal Nature Human Behavior, said the lidar detected a large, previously unknown, rectangular earth ceremonial space in San Lorenzo.

It measures about 1,000 meters by 275 meters, with 20 platforms around the edge slightly raised. Its purpose is not clear, but it is possible that it was a square in which a large number of people gathered to celebrate some type of ceremonies, while the platforms that surround the square could have housed residences, according to Inomata.

Lidar-based technology can be used to draw 3D images of ancient archaeological sites, such as Buenavista, in the Mexican state of Tabasco, at dawn.

Olmec heads, each formed from a single basalt rock, are among the most evocative pieces of art from ancient Mesoamerica. The naturalistic facial features are carved in such a way that experts suspect they are representations of ancient royal Olmec rulers.

Ten heads have been discovered in San Lorenzo. Inomata said there may be more of them undiscovered on related sites.

Many of the hundreds of ceremonial complexes identified in the study share common designs such as that of San Lorenzo. Many appear to have been built with orientations aligned with the direction of sunrise on key ceremonial dates.

“These centers were probably the first material expressions of the basic concepts of the Mesoamerican calendars,” Inomata said, noting that these calendars were based on a 20-day unit, which coincides with the number of platforms around the ceremonial center of San Lorenzo.

An even larger ceremonial center, described by Inomata and his colleagues, last year, was found at a site in the Mayan region called Aguada Fénix, in Tabasco, near the border with Guatemala. This center, which dates to slightly later than San Lorenzo, and others found in the study suggest that the Olmecs and other peoples of the region exchanged ideas.

Lidar has proven increasingly useful to archaeologists.

“The advantage of lidar is that it provides a three-dimensional view, from a bird’s eye view, of the landscape and of the modifications made by humans – ancient and modern – in the form of construction, transport, agricultural and water control infrastructures,” said the lidar engineer and study co-author, Juan Carlos Fernández-Díaz, from the National Center for Airborne Laser Cartography at the University of Houston.

“Lidar also allows us to ‘see’ the landscape and infrastructure that in many parts of the world are hidden under forest cover,” added Fernández-Díaz.