Danes rebuilt the mountains (5)
I believe the answer is:
andes
'the mountains' is the definition.
(I've seen this in another clue)
'danes rebuilt' is the wordplay.
'rebuilt' indicates an anagram.
'danes' is an anagram of 'ANDES'.
(Other definitions for andes that I've seen before include "South American mountain chain" , "Great S American mountains" , "Great mountains of western S America" , "South American mountain range" , "A geographical feature" .)