Severe party at ancient city (4)
I believe the answer is:
dour
'severe' is the definition.
(I've seen this in other clues)
'party at ancient city' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'at' means one lot of letters go next to another.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'do'+'ur'='DOUR'
(Other definitions for dour that I've seen before include "Obstinate - grim" , "Sullen - hard - obstinate" , "Gloomy in manner or appearance" , "Grim, morose" , "Stubborn" .)