The huge external stones of the Colosseum were fastened together using metal clips rather than cement during construction. The clips were removed from the stone works by "recyclers" when the building went out of use. The exterior is pock pitted with holes as a result.
As a result, gravity is the only factor holding these external walls together.
The Colosseum was also constructed in the first century. It had the most seats available of any sports venue in the world up to the 19th century.
The Colosseum, also known as the Flavian Theatre (for the imperial dynasty that oversaw its design and construction), was the greatest structure of its type and entertained many people as a diversion from their daily chores. It was also a clever stroke of imperial propaganda because it was constructed on the site of the Domus Aureus, the unpopular emperor Nero's imperial residence. They filled the pond that had previously been in the garden and the tiny stream that had been diverted to fill this pond in order to construct it. This would later be the reason why one side of the Colosseum collapsed in an earthquake as the soil there was far more loose than under the other part and thus suffered from liquification making the whole underground unstable.
