From the publisher's website:
In Colosseum you are a Roman impresario - producing great spectacles in your arena in the hope of attracting the most spectators to your events. You'll earn wealth and glory for each event you run, using it to build ever more ambitious events. Attract the most spectators to one of your events and you'll be granted the title of Grand Impresario, with tales of your extraordinary spectacles acclaimed throughout the empire. However, to produce larger events that will attract more spectators, you will need to build up your arena's infrastructure.