Why after the prepostion "unter" does the dative follow it?

I am very confused why after "unter" you use the dative case . For example: Unter dem Meer Why after that does the dative follow. Please can anyone explain this to me. Thank you

November 25, 2017


Unter takes either accusative or dative depending on usage.

November 25, 2017

Das ist ein guter Link. Danke!

November 26, 2017
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