HANOI, Vietnam (AP) _ Archaeologists announced Tuesday that they have uncovered the ruins of an ancient citadel in Hanoi dating back 1,300 years, describing it as the most important archaeological find in Vietnamese history.

Workers began clearing an area the size of two soccer fields in December 2002 to build government buildings, but archeologists were called in to investigate before construction began because it was believed the site may contain artifacts.

On Tuesday, an archaeological team revealed it had discovered thousands of artifacts, many in good condition, as well as pillar foundations of a structure, graves, a network of drainage systems, water wells and imprints of an ancient river and lake.

``This is the biggest and most important archaeological find in Vietnam's archaeological history,'' said Tong Trung Tin, deputy director of the Institute of Archaeology.

In some places, the team came across artifacts and structures built on top of each other ranging from the 7th to the 19th centuries, he said.

Tin said the excavation site covers only a small part of the western side of the citadel, which was believed to cover an area up to 345 acres under the Le Dynasty from the 15th to 18th centuries.

The team has another acre to clear, and was expected to finish in another four months.

Tin did not say when the discovery was made.

Minister of Culture and Information Pham Quang Nghi said Vietnam will seek UNESCO recognition of the area as a cultural heritage site but the government has not yet decided how to preserve the discovery.

``The find will help the Vietnamese people to better understand their age-old culture and history,'' he said. ``It also would be a major attraction to tourists.''

Tin said he will request international assistance for the project.

The new National Assembly Hall and the National Convention Center were originally scheduled to be built on the site.