I understand that ある means to live / to be. But I'm having trouble finding the purpose or translation of おしろに. I wonder if these two are working together to create some kind of meaning. It's from a children's book. The first line is むかし、(once upon a time), followed by the text above. My interpretation is that this means something to the effect of, "Once upon a time, there lived...". But I'm not understanding the specific action of the おしろに part of the sentence and so far haven't had luck with the dictionary. Any help is appreciated.
1 Answer
Before getting to おしろに, I'll talk about ある. The verb ある that you're thinking of means "to be / exist" but it's generally not used for living things. So it usually wouldn't mean "to live." Here it's not a verb, but a (probably etymologically related but different) ある that can only go before a noun and means "a certain ~"
As for おしろに, the core of it is しろ (castle).
In front of the core it has a kind of honorific / word-beautification marker お.
At the end is the location-marking particle に.
If we put everything together, あるおしろに means "in a certain castle."
Presumably the sentence continues with a description of someone living in the castle.
