Settled close around fort (9)
I believe the answer is:
ensconced
'settled' is the definition.
('ensconce' can be a synonym of 'settle')
'close around fort' is the wordplay.
'close' becomes 'end' (I've seen this before).
'around' indicates putting letters inside.
'fort' becomes 'sconce' (historical term for a fort or defence).
'end' enclosing 'sconce' is 'ENSCONCED'.
(Other definitions for ensconced that I've seen before include "Safely established" , "in safe seat" , "Settled comfortably" , "Installed" .)