The Sibillini Mountains, or Sibylline Mountains (Italian: Monti Sibillini) are one of the major mountain groups in the Italian Peninsula, and part of the Apennines range. Most of the peaks are over 2000m (7,000feet); the highest is Monte Vettore at 2476m (8,123feet).
Since 1993 the area has been part of the Parco Nazionale dei Monti Sibillini (Sibillini Mountains National Park).
The present-day landscape morphology, predominantly U-shaped valleys and glacial depressions, is due to the action of glaciers during the Quaternary period.
The name Sibylline goes back to a legend about a cave in the mountains (today known as the Sibyl cave), where a male oracle and necromancer took refuge to escape Christian persecutions against paganism in the late Roman period, and who occasionally revealed secrets of the future. Necromancers and knights travelled from across Europe, after exhausting journeys, to try to obtain a prophesy.
The small Lago di Pilato within a deep U-shaped valley below Monte Vettore, is home to a crustacean endemic to this location, Chirocephalus marchesonii.
The area contains stands of beech scattered amongst open subalpine grasslands and meadows maintained by the grazing of sheep.