A portion of the ridge forming the rim of the larger crater of the Alban volcano (see Albanus MoNs) and more especially the eastern portion, traversed by a narrow opening (now called the Cava d'Aglio) of which the Via Latina took advantage, and which frequently appears in the early military history of Rome. That a distinct town existed (Dion. Halic. x. 21, xi. 3) on the mountain is improbable; there must have been a fortified post, but the extensive castle on the hill (Maschio d'Ariano) to the south of the Via Latina is entirely medieval, a fact which has not been recognized by some topographers.