According to the legend, in early 1428, Emperor Lê Lợi was boating on the lake when a Golden Turtle God (Kim Qui) surfaced and asked for his magic sword, Heaven's Will. Lợi concluded that Kim Qui had come to reclaim the sword that its master, a local God, the Dragon King (Long Vương) had given Lợi some time earlier, during his revolt against Ming China. Later, Emperor Lợi gave the sword back to the turtle after he finished fighting off the Chinese. Emperor Lợi renamed the lake to commemorate this event, from its former name Luc Thuy meaning "Green Water". The Turtle Tower (Tháp Rùa) standing on a small island near the centre of lake is linked to the legend. The first name of Hoàn Kiếm lake is Tả Vọng, when the King hadn't given the Magical Sword back to the Golden Turtle God (Cụ Rùa).