The port is a local one (4)
I believe the answer is:
bari
'the port' is the definition.
(I've seen this before)
'local one' is the wordplay.
'local' becomes 'bar' (local can mean someone's local pub).
'one' becomes 'i' (Roman numeral).
'bar'+'i'='BARI'
'is a' acts as a link.
(Other definitions for bari that I've seen before include "Adriatic seaport" , "Adriatic port" , "Adriatic resort" .)