Surrounded by numbers of Romans (3)

I believe the answer is:

mid

I'm a little stuck... Click here to teach me more about this clue!

'surrounded' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?

I cannot 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 "Prefix meaning centre" , "Of the central part" , "Dim sort of prefix" , "Denote the centre point" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.