City of the Ruhr (5)
I believe the answer is:
'city of the ruhr' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for essen that I've seen before include "German industrial centre" , "German industrial city on the Ruhr" , "Industrial city of northwest Germany" , "European city" , "Krupp HQ (Ger.)" .)