Located just inside the Porta San Sebastiano on the Via Appia, the so-called Arch of Drusus actually is part of the Aqua Antoniniana, constructed by Caracalla to supply water to his baths. Here, the archway is more ornamental than the rest, as was typical when an aqueduct crossed a road. Revetted with white marble and decorated with columns of Numidian marble with Composite capitals placed on pedestals, the entablature was surmounted by a pediment, a remnant of which still can be seen. The aequeduct itself terminated in a large reservoir, where the water flowed through a number of cisterns, depositing its sediment and becoming heated.
The name derives from the fact that the Notitia identifies an Arch of Drusus in Regio I that was erected by the Senate, which "voted him a marble arch adorned with trophies on the Appian Way, and the surname Germanicus for himself and his descendants" (Suetonius, Life of Claudius, I.3; also Dio, LV.2.3).
