The Ernici Mountains are a mountainous chain belonging to the Lazio subapennines that stretches in an east-west direction and is delimited to the north by the Aniene Valley, to the east by the Liri Valley and to the south and west by the valleys of Cosa and Sacco. They form the natural border between Lazio (north Ciociaria) and Abruzzo and as a consequenze the west facing slopes are less steep and undulating while those facing east are steep.