In Vietnamese ha long means descending dragon’, and legend has it that Halong Bay was formed by a gigantic dragon which plunged into the Gulf of Tonkin, creating thousands of limestone outcrops by the lashing of its tail. Geologists tend to dismiss this theory, arguing that the myriad islands that dot Halong Bay and extend all the way north to the Chinese frontier are the product of selective erosion of the seabed over millennia.