For those, who never have been in Rome, a "must" is to see the Colosseo. You don't need to go inside, but you have to understand the (sad) history of that magnificent building, one of the new 7 wonders! We could start from the capitol hill, from there you have a good sight to the Forum Romanum. The time we have saved, we would need now to walk from the colosseo alongside Circo Massimo and the Palantine Hill versus Teatro Marcello and other amazing ancient monuments.