Near the northern shore of the Hoan Kiem Lake (Lake of the Returned Sword) lies Jade Island on which the Temple of the Jade Mountain (Ngoc Son Temple) stands. The temple was erected in the 18th century. It honors the 13th-century military leader Tran Hung Dao who distinguished himself in the fight against the Yuan Dynasty, Van Xuong, a scholar, and Nguyen Van Sieu, a Confucian master and famous writer in charge of repairs made to the temple in 1864. https://en.wikipedia.org/wiki/Ho%C3%A0n_Ki%E1%BA%BFm_Lake