Gladiatorial sites
I believe the answer is:
arenas
'gladiatorial sites' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for arenas that I've seen before include "Sports venues" , "Areas of endeavours" , "Areas for events, sporting perhaps" , "Sites of gladiatorial combat" , "Level areas in centre of sports stadiums" .)