Surrounded by Roman figures (3)

I believe the answer is:

mid

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'surrounded' is the definition.
Both the answer and definition are adjectives. Maybe there's an association between them I don't understand?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for mid that I've seen before include "Dim sort of prefix" , "Prefix meaning centre" , "Of the central part" , "Denote the centre point" .)

I've seen this clue in The Globe and Mail.

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