The Colosseum of course needs no introduction. It's the template for all the football and soccer stadia around the world, and its incredibly violent games and bloodthirsty mob of spectators are a stock feature of every film about ancient Rome. As a ruin, it makes an incomparable impression. Even two thousand years later the elegance and sheer size of the thing, plus the fact that it largely survived the ravages of time and the rapacious Romans of later years, is awe inspiring. As you tour the holding pens for the animals, slaves and gladiators who would all fight and die here for the crowd's amusement, tanks to catch the runoff of all the blood and the plumbing system that allowed the place to be flooded for naval battles, it's very easy to picture what it must have been like when it was in use and people and animals slaughtered more or less continually just for fun.