In 2009, during preliminary excavations for the station at Piazza Venezia (near the Capitoline Hill) workers found remains of what has been identified as emperor Hadrian's Athenaeum.

[11] Initially, the planned termini were Pantano (a frazione of the comune of Monte Compatri) in the east and Clodio-Mazzini in the north, but in March 2007, a northward extension along the Via Cassia was announced, with nine more stations to Grottarossa.

[12] Instead, a portion of the ruins of the barracks used by the Praetorian Guard will be viewable through a large glass window.

[13] The initial plan featured a station at Largo di Torre Argentina in the city center.

[14][better source needed] The following extensions have been studied: Line C is served by 30 AnsaldoBreda Driverless Metro convoys.