<P> Ha Long Bay has an area of around 1,553 km, including 1,960--2,000 islets, most of which are limestone . The core of the bay has an area of 334 km with a high density of 775 islets . The limestone in this bay has gone through 500 million years of formation in different conditions and environments . The evolution of the karst in this bay has taken 20 million years under the impact of the tropical wet climate . The geo - diversity of the environment in the area has created biodiversity, including a tropical evergreen biosystem, oceanic and sea shore biosystem . Ha Long Bay is home to 14 endemic floral species and 60 endemic faunal species . </P> <P> Historical research surveys have shown the presence of prehistoric human beings in this area tens of thousands years ago . The successive ancient cultures are the Soi Nhu culture around 18,000--7000 BC, the Cai Beo culture 7000--5000 BC and the Ha Long culture 5,000--3,500 years ago . Ha Long Bay also marked important events in the history of Vietnam with many artifacts found in Bai Tho Mountain, Dau Go Cave, Bai Chay . </P> <P> 500 years ago, Nguyen Trai praised the beauty of Ha Long Bay in his verse Lộ nhập Vân Đồn, in which he called it "rock wonder in the sky". In 1962, the Ministry of Culture, Sports and Tourism of North Vietnam listed Ha Long Bay in the National Relics and Landscapes publication . In 1994, the core zone of Ha Long Bay was listed as a World Heritage Site according to Criterion VII, and listed for a second time according to Criterion VIII . </P> <P> The name Ha Long means "descending dragon". </P>

When did ha long bay become a world heritage site