Ancient city found on Mexican farmland.

Draped by citrus orchards and banana plantations near Mexico's Gulf Coast,

archaeological remains long considered the vestiges of several small human set- tlements have been found to derive instead from a massive city that served as a center of regional trade and culture beginning around 1,600 years ago, according to an archaeologist who directed a survey of the area last year.

Excavation of the site, known as El Pital, has yet to begin. But surface explorations indicate that the metropolis grew rapidly from A.D. 100 to A.D. 600, at which point overwhelming floods or warfare may have led to its abandonment, asserts S. Jeffrey K. Wilkerson, director of the Institute for Cultural Ecology of the Tropics in Gutierrez Zamora, Mexico.

Wilkerson discussed the find at a Mexico City press conference last week and in a subsequent telephone interview with SCIENCE NEWS.

El Pital hit its stride as ancient civilizations in Mexico and Central America entered their Classic Period, which extended from about A.D. 300 to A.D. 900, Wilkerson contends. But the once majestic city hit the skids midway through the Classic era.

"El Pital appears to have been an early city of astounding proportions that achieved great complexity by the start of the Classic Period," Wilkerson argues. "We don't know what sparked the rise of Classic civilizations, but we're on the trail of some answers at El Pital."

The city core, located on the Nautla River in the eastern Mexican state of Veracruz, contains more than 100 earthand-stone structures. These include small buildings, elongated platforms, ball courts, and massive temples, some of which reach heights of 130 feet. Banana, citrus. and sugar-Cane plantations, as well as thick flood sediments, obscure much of the site.

Satellite communities and an elaborate system of irrigation canals threading through raised fields for farming cover 40 square miles around the site.

Ceramics and other artifacts at El Pital indicate that it lay at the hub of a regional trade network and maintained cultural ties to cities of central Mexico, including Teotihuacan, Wilkerson maintains. Teotihuacan exerted considerable influence throughout the region for much of the first millennium A.D.

El Pital's links to Classic Maya cities, which arose at the same time some 500 miles to the southeast, remain unknown, the archaeologist notes.

The lack of defensive structures at El Pital suggests that a powerful royal dynasty governed a broad region organized around commerce, he says. The city may have served as a major seaport, given its proximity to two easily navigable rivers that run nine miles to the ocean, Wilkerson says.

El Pital somewhat resembles El Tajin, a nearby Classic-Era city. But the latter site was smaller and reached its peak betweenA. D. 600 and A.D. 1100.

Wilkerson hopes to test whether severe weather fluctuations -- thought by some researchers to occur in the Americas about every 500 years -- caused excessive rainfall and coastal flooding, thus influencing El Pital's demise and hastening El Tajin's rise.