Lóngyuān (龍渊) is the former name of Lóngquán (龍泉), a town along the Ou river in Zhejiang province, China, known for its sword making.
The founder of the Tang dynasty, Emperor Gaozu, banned the use of the character yuān as it was part of his personal name and thus it came to be known as Lóngquán.
Yuān means a deep pool, or "deep/profound" in meaning. Before this event, swords from lóngquán could also be called yuān jiàn (渊劍); "deep well sword".
An old set of double swords with an inscription that refers back to the town's past name.
Sold by Mandarin Mansion in 2021.
"Deep well sword"
Another sword with a reference to the town's old name is published by Alex Huangfu.1 The markings include the words:
Lóngquán yuān jiàn
"Lóngquán deep well sword"
Qiān Zì Hao
"Thousand Mark Brand"
1. See Alex Huangfu; Iron and Steel Swords of China. (皇甫江; 中国刀剑). Jinan, Tomorrow Publishing House, 2007. Page 225.
See my glossary article: Lóngquán (龍泉)