Rex intially wrecked us in wrecks (5)
I believe the answer is:
ruins
'wrecks' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ruins that I've seen before include "Derelict buildings" , "Remains to be seen" , "Mars" , "Wrecks" , "Damages beyond repair" .)