Port one found in barrels (5)
I believe the answer is:
tunis
'port' is the definition.
(I've seen this before)
'one found in barrels' is the wordplay.
'one' becomes 'i' (Roman numeral).
'found in' indicates putting letters inside.
'barrels' becomes 'tuns' (tun is a kind of barrel).
'i' inserted within 'tuns' is 'TUNIS'.
(Other definitions for tunis that I've seen before include "Mediterranean capital and port" , "N African port" , "Tom, Dick or Harry" , "Carthage lies near this N. African city" , "North African location" .)