Detail embroidered on front of carpet for fortress (7)
I believe the answer is:
citadel
'for fortress' is the definition.
(citadel can mean a fortified city)
'detail embroidered on front of carpet' is the wordplay.
'embroidered' indicates an anagram.
'on' says to put letters next to each other.
'front of' says to take the initial letters (the letter at the front of the word).
The initial letter of 'carpet' is 'c'.
'detail' with letters rearranged gives 'itadel'.
'itadel' after 'c' is 'CITADEL'.
(Other definitions for citadel that I've seen before include "Stronghold usually within the walls" , "Kremlin" , "Fort, fastness" , "Urban fortress" , "Keep - castle" .)