Capital city’s outskirts evacuated, behold (4)
I believe the answer is:
oslo
'capital city's' is the definition.
(capital of Norway)
'outskirts evacuated behold' is the wordplay.
'evacuated' says to hollow out the word (remove centre letters) (internal letters are evacuated from the word).
'behold' becomes 'lo' (archaic exclamation meaning 'look!').
'outskirts' with its middle removed is 'os'.
'os'+'lo'='OSLO'
(Other definitions for oslo that I've seen before include "Capital often frozen" , "Nordic capital" , "where Ibsen lived under another name" , "Norway's capital city" , "Former Christiania" .)