What's the meaning of との in this sentence?
Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.Sign up to join this community
It's a case particle と ("with" as in "face with something" or "fight with someone") followed by a noun-linking particle の. See:
Assuming this sentence is said in a common fantasy RPG-like setting, 後衛との壁 refers to either of:
The former is more likely but it may mean the latter depending on the context.