The smaller islands of the Tuscan archipelago are—Giglio, with quarries of granite; Monte Cristo, a pyramidal rock rising 2,130 feet above the sea-level; Pianosa, with an agricultural penal settlement; Capraja, with a small town built within an amphitheatre of pink-coloured granite; and Gorgona (987 feet).[87] {257} V.—THE ROMAN APENNINES, THE VALLEY OF THE TIBER, THE MARCHES, AND THE ABRUZZOS. That portion of the Italian peninsula which has Rome for its centre may be likened to the trunk of the body, for it is there the Apennines attain their greatest height, and nowhere else to the south of the Po are rivers of equal magnitude met with.[88] The main rampart of the Apennines runs parallel to the coast of the Adriatic. To the mariner, who sees these mountains rise above the verdure of the littoral region, they have an appearance of the greatest regularity. Summit rises beyond summit, one lateral chain succeeds to the other, and every one of the numerous valleys descends perpendicularly to the coast. The slope throughout is steep, and the geological strata, whether of Jurassic, cretaceous, or tertiary age, succeed each other regularly from the snow-clad summits down to the promontories of the coast. The only irregularity consists in a detached group of hills (1,880 feet) to the south of Ancona, above which the axis of the Apennines changes its direction. This region of Italy is the natural counterpart of Liguria. The position of Ancona corresponds with that of Genoa, and the coast, which extends on the one hand to Emilia, and on the other towards the peninsula of Monte Gargano, may fairly be likened to the “Rivieras” of Genoa, with this exception, that its direction is inverse. The territory between the mountains and the coast is narrow, the littoral road frequently winds round promontories, and the towns extend up the hill-sides. Still this portion of Italy is not as strongly protected by nature as Liguria. Towards the north it expands upon the plain of the Po, whilst the terraces at the foot of the main range of the Apennines afford easy access from the west. During the whole of the Middle Ages and down to our own days neighbouring states have fought for the possession of this territory, which has become known, from this circumstance, as the “Marches;” that is, the disputed frontier districts, where every town is a fortress perched on the top of a hill.