King of Rome heard in ruins (6)
I believe the answer is:
wrecks
'ruins' is the definition.
(wrecking is a kind of ruining)
'king of rome heard' is the wordplay.
'king of rome' becomes 'rex' (I've seen this in another clue).
'heard' indicates a 'sounds like' (homophone) clue.
'rex' sounds like 'WRECKS'.
'in' acts as a link.
(Other definitions for wrecks that I've seen before include "Ships destroyed at sea" , "Ships at bottom of sea" , "Ships on sea bed" , "suffers ruin" , "ruins" .)