Rome's main airport is well-connected to the center during the day by a direct train and slower trains. At the ticket window by the platform at Fiumicino. Use the Tiburtina station stop to reach the center. They take 46 minutes to reach Tiburtina. A smaller airport dealing mainly with charter flights and budget airlines.
Buses leave every half hour.
Fiumicino For arrivals and departures between 11.30pm and 5am, there is a night bus running between Fiumicino and Tiburtina station. It stops at Termini Station. The 40N bus connects Tiburtina and Tremini during the night. Ciampino Buses connecting Ciampino airport with the center of Rome stop running at 11pm, so the only way to get into town late at night is by taxi. After having exited the arrival hall at Fiumicino, you will find the taxi rank.