Excursion in direction of ancient city (4)
I believe the answer is:
tour
'excursion' is the definition.
(I know that excursion can be written as tour)
'in direction of ancient city' is the wordplay.
'in direction of' becomes 'to' (heading to).
'ancient city' becomes 'ur' (ancient Sumerian city state).
'to'+'ur'='TOUR'
(Other definitions for tour that I've seen before include "Travel around" , "Go round" , "Trip visiting several places" , "Rout on excursion" , "Short trip; spell of duty" .)