Temple of the Jade Mountain (Ngoc Son Temple) in the central Ha Noi’s Hoàn Kiếm Lake is dedicated to Confucian and Taoist philosophers and to the Vietnamese national hero Trần Hưng Đạo (b 1228 – d 1300). When the temple was built sometime in the 18th century it was just a small temple, but after an expansion in 1865 more buildings were added.
Hoàn Kiếm Lake (the name of the lake in English means something along the lines of “Lake of the returned sword”), the lake has had different names over time, one of them in English was the “Green water lake” which refers to the color of the water in the shallow lake, the depth is between 1.2 and 2 meters.
Today the centrally located lake and it’s surroundings is a gathering place for locals as well as for tourists. The lake is also a part of a legend that includes Vietnam’s greatest hero and one of the most famous persons in Vietnamese history Emperor Lê Lợi.
The legend starts in the Thanh Hóa province, some 150 km south of Ha Noi. During his evening fishing expedition on the local lake, fisherman Lê Thận caught something heavy in his nets and felt excited about such a big catch. The catch turned out not to be a big fish, but just a piece of metal. Disappointed, he threw the piece of metal back into the water and cast his net again. When he pulled the net in, he found that the piece of metal had yet again made its way back into his net. He mustered all his strength and threw the piece of metal back into the water, this time far away enough that he felt certain that it could not make it’s way into his net again. However, after casting his net again with the same result – the piece of metal was once again in his net, he shun his light on the piece of metal and then he realized that it was in fact the blade of a sword. He brought the blade with him home after his fishing expedition ended and put it away in a corner in his house.
A few years later Lê Thận joined the army of the rebel leader Lê Lợi to fight against the Chinese incursion into Vietnam, he was very successful on the battlefield and quickly rose through the ranks. The warrior Lê Thận caught the eye of the general and the two became friends. When general Lê Lợi visited Lê Thận at his home, the dark home suddenly became lit up from the glow of the sword blade that was sitting in the corner where Lê Thận had placed it after he brought it home. Lê Lợi felt that this had somehow come about as a result of his presence in the home and he grabbed the blade and held it up to look at it. Before his eyes the words “Thuận Thiên” (Will of Heaven) appeared on the blade. With the permission of Lê Thận, general Lê Lợi brought the blade with him when he left.
One day while fighting the Chinese enemies, general Lê Lợi saw a Banyan tree up on a hill that was emitting a strange glow from it’s branches. He climbed the hill and under the Banyan tree he found the hilt of a sword. It was beautifully decorated with precious gem stones. He immediately thought of the sword blade he had brought from the home of Lê Thận, and brought it out and placed the hilt on the blade. It was a perfect fit. Lê Lợi thought this was a sign from heaven that he had been chosen to free the land, so he rallied his troops and went to war to drive the Chinese out of Vietnam. The sword helped them win many battles against the Chinese and they finally drove them out of Vietnam. Lê Lợi ascended the throne as emperor of Vietnam in 1428 (Emperor Lê Lợi ruled Vietnam 1428–1433).
Later when emperor Lê Lợi was in a dragon boat on the Hồ Lục Thủy (Green water lake). The lake was located just in front of the emperor’s palace, and according to the legend, a Golden Turtle God (Kim Qui) came to him and asked him for his magic sword. Lê Lợi assumed that the Golden Turtle God was acting on orders from the Dragon King who was seeking to reclaim the sword that he had given to Lê Lợi during his fight against the Chinese. When the emperor looked down at the sword in his belt he saw it starting to move on its own. The Golden Turtle God came up next to to the emperor in the boat and with a human voice asked him to give the sword back to the Dragon King. Emperor Lê Lợi then realized that the sword had just been lent to him to free the land and that it should be returned to the Dragon King who lives under water in the lake. He then threw the sword towards the golden turtle and the turtle caught it in his mouth and disappeared. In commemoration of this event the lake was renamed from Luc Thuy “Green Water Lake” to the current Hoàn Kiếm Lake (Lake of the returned sword).
The turtles in the lake are likely of the species Rafetus Swinhoe (Yangtze giant soft-shell turtle) , although some Vietnamese biologists claim that the turtles in the Hoan Kiem lake is a distinct species separate from the Rafetus Swinhoei species. If it is a separate species it is at this time extinct since the last known turtle in the lake died in 2016 and is embalmed and on display in the temple. Of Rafetus Swinhoei there are only three known specimen in the world that are known to be alive.