The Colosseum is just beside the Roman Forum and is probably an even bigger attraction though it is just a single building. It was started by Emperor Vespasian in 72 AD and completed in 80 AD, taking just 8 years - a remarkable feat considering the size and scale of the building. Clad in white marble and more then 10-storeys high, accommodating 87,000 spectators - it must have been quite a spectacle in its days. Even today it is an awe-inspiring sight.
The Colosseum was a political tool of the Emperor - built to provide free entertainment to the public in a bid to increase the Emperor's popularity. Of course we all know what happened in these arenas of doom - where gladiators fight to their death and thousands of animals were killed just for the sake of entertaining the masses.
Putting aside images of the blood bath that must have happened here - the Colosseum is an ingenious feat of engineering and architecture. Amazingly it is still the largest amphitheatre in the World according to the Guinness Book of Records.