Roman quartet retracing a Roman road (3)

I believe the answer is:

via

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'roman road' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for via that I've seen before include "By means of" , "By way of - in Latin" , "A Roman way" , "Going through" , "Roman road" .)

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

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