Fortress constructed at the front with elaborate detail (7)
I believe the answer is:
citadel
'fortress' is the definition.
(citadel can mean a fortified city)
'constructed at the front with elaborate detail' is the wordplay.
'at the front' suggests taking the first letters.
'with' means one lot of letters go next to another.
'elaborate' is an anagram indicator (I've seen this in other clues).
The initial letter of 'constructed' is 'c'.
'detail' is an anagram of 'itadel'.
'c'+'itadel'='CITADEL'
(Other definitions for citadel that I've seen before include "Urban stronghold - dialect (anag)" , "Keep - castle" , "Fortress (in or near city)" , "Urban fortress" , "Fort, fastness" .)