[A_Brandybuck]

Tolkien used intertextuality in a great way. He took much stuff, which he elaborated in his world, of the nordic mythology. One example is the ring.

A ring, especially a golden ring, was often used in mythologies. Mostly the ring is a symbol of something evil or bad. There was a magic ring, which was possessed by a Dwarf in a part of the Edda. The ring was stolen by a "God" and became the source of a dragon-hoard. The connections to Tolkien are obvious.
In the "Nibelungen", an old German myth, there was the "Ring of the Nibelungen", which brings his owner more power. But this Ring was cursed, too.

I think, that there is more stuff like this, but I need time to look it up and put it into the right context. ;-)