Colosseum 

Now what's there to tell... Built by emperor Vespasianus in 72 AD, but he didn't live to see the result. Rome's biggest amphitheater. In here, free performances with mortal fights between gladiators or wild animals. Fights with gladiators were prohibited as from 404 AD, with animals as from 523 AD. Room for 55.000 peeps. Decay due to time, neglect, re-use of travertin stone for other Roman buildings and thievery. Still very impressive though! Other Roman amphitheaters can be found in Tunesia, France (I also visited one in Nîmes) and North-Italy.
And now I'll let the pix speak for themselves...