'The Gunslinger,' as well as the rest of the Series, was influenced by one poem. 'Childe Roland to the Dark Tower Came' was written by Robert Browning, and built into a fascinating realm made by Mr. King.
Why not read it? I personally like it a lot...
Childe Roland to the Dark Tower Came
'The Waste Lands', by T.S. Elliot, was also a source of inspiration for 'The Waste Lands,' by Mr. King.
I absolutely love this poem. Read it...