Dutch city (6)
(Another definition for leiden that I've seen is " Dutch city with old university".)
'dutch city' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for arnhem that I've seen before include "place noted for fighting" , "Netherlands scene of 1944 battle" , "Site of 1944 battle" , "Dutch city" , "Location of battle" .)