Wikipedia tells us that the Vietnamese believe that the dragon gods threw a bunch of their jewels into the water in order to frustrate the invading armies from China.
The dragon jewels became islands in the sea.
We were there, about 10 years ago, visiting Vietnam with a close friend, her sister, her children, and her uncle. The uncle became my very best Communist friend.
We had a good time. Found a passable hotel. Ate a lot of good seafood. And, had a drink of something from a big jug with a pickled snake inside. I was supposed to feel healthy afterwards.