The dates vary as to when Tolkien started his Legendarium. Anyways – it was way before the film Metropolis but even the novel.
Mary Gentle has written several “steampunk”/”alternative history” novels. Some are collected in the book White Crow.
I have to confess that I’m not a Tolkien – ist. I know his novels from them being read to me at Junior School by Mrs Bagguley, our teacher. The last half hour of the school day we had The Hobbit and another one.
I know he was an Inkling at University.
I know that he was Steeped in myth and legend.
This video here has been a true eye-opener for me.