Saint in front of station inside the city walls (7)
I believe the answer is:
swithin
'saint' is the definition.
(saint swithun/swithin)
'front of station inside the city walls' is the wordplay.
'front of' says to take the initial letters.
'inside the city walls' becomes 'within'.
The initial letter of 'station' is 's'.
's'+'within'='SWITHIN'
'in' is the link.
(Other definitions for swithin that I've seen before include "Saint associated with weather (I not U)" , "Saint; with sin (anag,)" .)