Modern fortified building in English city (9)
I believe the answer is:
newcastle
'english city' is the definition.
(I've seen this before)
'modern fortified building' is the wordplay.
'modern' becomes 'new' (associated in meaning).
'fortified building' becomes 'castle' (I've seen this before).
'new'+'castle'='NEWCASTLE'
'in' acts as a link.
(Other definitions for newcastle that I've seen before include "town" , "Tyneside city" , "port for England" , "City on the Tyne" , "Man City?" .)