Which mountain range forms the spine of the Italian Peninsula?

The Apennine Mountains form the spine of the Italian Peninsula.

The Apennines run for roughly 1,200 kilometres from the Ligurian Alps in northwestern Italy to Calabria in the south. Their long chain of parallel ridges divides the peninsula into eastern and western sides and gives Italy much of its familiar elongated, mountainous shape.

The range is not a single narrow wall. It contains several sections, including the Northern, Central and Southern Apennines, with geology shaped by folding and thrusting. Corno Grande, in the Gran Sasso massif, is the highest summit at 2,912 metres.

The Alps border Italy across the north, but they do not run down the length of the peninsula. That is the key distinction in this question: the Alps form Italy’s northern mountain frontier, while the Apennines continue through the country’s central backbone. The range also crosses parts of San Marino and extends toward Sicily through the Sicilian Apennines.