 In 938, a Southern Han fleet entered Vietnam by sea via the Bạch Đằng estuary (mouth of the river which flows into Hạ Long Bay).Ngô Quyền ordered iron-tipped stakes to be planted into the riverbed.At high-tide, a Vietnamese flotilla attacked the enemy then, pretending to escape, lured the Han ships into the water where the stakes, still covered by the tide, are beneath.