The Apennine Mountain Range (Apennino) forms the backbone of peninsular Italy. Approximately 870 miles long, its highest peak reaches 9,560 ft. It runs from Liguria in the north west to Calabria in the south west, the mountains of Sicily being its continuation. Being lower they differ geographically from the Alps, having no glaciers and being more exposed to maritime influence. They are geologically oldest in the south. On their western edge, from Tuscany to Sicily, severe faulting has given rise to a series of volcanoes including, notably, the active Mount Vesuvius near Naples and Mount Etna in Sicily. Ruskin first wrote about the mountains without having seen them in The Poetry of Architecture (1837-38), describing the effect of their geology on regional architectures ( Works, 1.110).