The
Sibillini Mountains, or Sibylline Mountains (
Italian:
Monti Sibillini) are a mountain group in
Italy, part of the central
Apennines. Situated between eastern
Umbria and the
Marche, they are mostly composed of
limestone rocks, formed in the
Mesozoic and
Cenozoic (100 to 50 million years ago) on the bottom of an extinct sea. The land emerged 20 million years ago. Most of the peaks are over ; the highest altitude is reached by
Monte Vettore at .