Upon the river or under the river?

Question

Why are some towns in the UK called Town upon River e.g. Newcastle upon Tyne and why are some called Town under River e.g. Newcastle-under-Lyme? What's the difference? How can a town be under a river? What does it mean?

Answer 1

It isn't literal. I think a lot of those are old names that reference the geographical proximity to a river. Upon probably means the river runs through the town and under might mean the town is south of the river.

I'm kinda guessing here. But it makes sense to me.

Answer 2

Actually she's right. It's a descriptive term relating to the original town and it's position to the river. "Upon" means the tows crosses the river, there "under" means the town is south of the river. This also related to mountains such as "Stratford upon Avon", there Shakespear lived.