One revered before the first year of Our Lord, I'm thinking, in the Colosseum? (7)
I believe the answer is:
stadium
'colosseum?' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stadium that I've seen before include "Sports arena" , "Admit us (anag) - sports ground" , "eg Yankee, Wembley" , "Venue for sporting events, concerts etc" , "bowl?" .)