Alban deployed to Sumerian city walls in capital (4,5)
I believe the answer is:
ulan bator
'capital' is the definition.
(capital of Mongolia)
'alban deployed to sumerian city walls' is the wordplay.
'deployed' indicates anagramming the letters.
'sumerian city' becomes 'Ur' (ancient Sumerian city).
'walls' indicates putting letters inside (to 'wall' can mean to contain).
'alban' is an anagram of 'lanba'.
'lanba'+'to'='lanbato'
'lanbato' inserted into 'ur' is 'ULAN BATOR'.
'in' acts as a link.
(Other definitions for ulan bator that I've seen before include "capital city" , "Capital of Mongolia" , "Mongol city" , "Mongolian city" , "Exotic capital" .)