Ostia is a 25 minute train ride away from Rome. Back in the ancient times, it was the port city of Rome. So traders and imports from foreign countries would come to Ostia before going to Rome. It use to be a really active city, but then as the Roman Empire was weakening, Ostia lost it's purpose and wealth, so was then abandoned. Because it was simply abandoned, it is one of the best preserved cities of the Roman Empire (but Pompeii is better preserved because a Volcano eruption literally covered the entire city, including the people, and I will be going there soon so look out for more pics!)