Underneath the jungle curtain of mud and dense foliage was a sprawling lost city called "Cancuen," (can-ku-win), one of the most important commercial centers of the Mayan world for more than 1,200 years.

Cancuen has been rediscovered by Guatemalan and American scientists working deep in the country's northern jungles. They believe it will take 10 years to fully unearth the city, which dates to 400 B.C.

It is buttressed by a 270,000-square-foot Mayan palace. With three floors - each 66 feet high - and 170 rooms, it is among the most grandiose Mayan structures ever discovered, the National Geographic Society announced Friday.

The society is a chief sponsor of the Cancuen excavation project.

"We started off working with what we thought was a small palace, part of a small Mayan settlement," said Arthur Demerest, a Vanderbilt University archaeologist and head of the Cancuen project. "What we found was a palace 20 times as large as we were expecting and an important Mayan marketplace that had been forgotten for almost 100 years."

Built in the shadow of the hulking palace, the 5-square-mile city featured a crowded rectangular layout of heavy stone walls, 11 spacious stone-tiled patios and buildings with cubbyhole-like rooms and thick, multileveled roofs.

While Demerest said scientists aren't sure how many Mayan merchants traded in Cancuen, the city is thought to have attracted thousands from nearby highland settlements, including the sprawling, majestic city of Tikal, 85 miles to the northeast.

Cancuen, an ancient Maya word meaning "Place of the Serpent," became a key trading post because of the sprawling River Passion in what is known today as southern Peten, Guatemala's northernmost province, Demerest said.

First discovered in 1905 by Austrian explorer Tobert Maler, scientists and looters ignored the site for years.

"A city that was built only for commercial purposes and not for religious ones seemed uninteresting to a lot of academics and worthless to a lot of looters," Demerest said, adding that the city is now overrun with such jungle-dwelling animals as howler monkeys.

Cancuen lacked the breathtaking temples that dominate Tikal and other Mayan sites because its inhabitants worshipped and buried their dead in surrounding highland areas.

"All of the fantastic temples you see at other sites are an effort to copy the altitude of the highlands that surrounded Cancuen," said Demerest, who said that being close to the heavens was the cornerstone of Mayan religious practices. "In Cancuen they had the real thing."

Though work at the site has been suspended until next spring because of the rainy season, scientists have already recovered dozens of artifacts in nearby mountain caves.

Cancuen remained shrouded by jungle until 1967, when a group of Harvard graduate students returned to the city for less than a week and brought back crude sketches of what they thought was waiting to be discovered there.

Demerest and scientists from Guatemala's City's Valley University were drawn back to the area in April because hieroglyphics inscribed in artifacts recovered in Tikal and Dos Pilas, the ancient Maya's largest commercial center, made reference to a marketplace called Cancuen and its powerful fourth-century B.C. ruler, Tah Chan Wi, or "Celestial Fire."

Frederico Fahsen, the foremost Guatemalan authority on deciphering Mayan hieroglyphics and the Cancuen project's co-director, said the Cancuen ruler married his daughter to the king of Dos Pilas, 55 miles to the northeast, to establish relationships with surrounding settlements rather than go to war with them.

"Mayan cities have been in constant war, with their constructions dedicated to the gods and the heavens," Fahsen said. "Here we have exactly the opposite."