By way of the Roman road (3)
I believe the answer is:
via
I believe this is a triple definition!
'by' is the first definition.
(thesaurus)
'way' is the second definition.
(I've seen this in other clues)
'of' is a link.
'the roman road' is the third definition.
(I've seen this before)
(Other definitions for via that I've seen before include "Going through" , "A Roman way" , "Passing through" , "Roman road" , "By means of" .)