It shows the importance of History in the past.
The colosseum is in the country of Italy. In the city of Rome to be exact.
There isn't sorry you have to do it the long way round
No totodile is not available in sapphire you will need to trade one from Emerald or Pokemon XD Gale of Darkness also you can breed the shadow Crocanaw from Pokemon Colsseum to get totodile as well.
In Pokemon colociem you can catch Pokemon like charizard,pikachu,pidgey,not realy Pokemon in diamond and pearl or plattinum or emerald, sappire, and ruby. plus you will find some from Pokemon red ,green ,yellow and so on.point is you will find the old type of Pokemon in the old Pokemon shows.