Help me please with this poem
Three rings for the elven kings under the sky,
Seven - for the dwarf lords in their halls of stone,
Nine - for mortal men, doomed to die,
One - for the Dark Lord on his dark throne,
In the land of Mordor, where the shadows lie.
One Ring to rule them all, One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the land of Mordor where the shadows lie.
What's the metre of this verse?
Thank you very much in advance!