Article about ancient city united Pacific island (5)
I believe the answer is:
nauru
'pacific island' is the definition.
(I've seen this before)
'article about ancient city united' is the wordplay.
'article' becomes 'an' (English indefinite article).
'about' shows that the letters should be reversed in order.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'united' becomes 'U' (abbreviation).
'an' in reverse letter order is 'na'.
'na'+'ur'+'u'='NAURU'
(Other definitions for nauru that I've seen before include "Fairground carousel" , "Smallest Pacific state" , "Pacific island country" , "SW Pacific republic" , "Pacific republic, formerly Pleasant Island" .)