Council site of 1545
I believe the answer is:
trent
'council site of 1545' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for trent that I've seen before include "Main river of the Midlands" , "Midlands banker" , "Eng. river; Council of -" , "Nottingham's river" , "River through Newark" .)