The city is built, as we have shown in our first chapter, on one of the low hills formed after thousands of years by the silting up of the refuse brought down by the Tiber, and not, as one naturally at first imagines, on a spur of the actual Apennines which are divided from her by the river. Much of the power of the town in the past may be traced to her extraordinary topographical position. Perugia stands 1705 feet above the level of the sea, and 1200 above that of the Tiber. She stands perfectly alone at the extreme edge of a long spine of hill, and she commands the Tiber and the two great roads to Rome.[43] But looked at from a merely picturesque point of view, few towns can boast of a more powerful charm. Perugia, if one ignores her history, is not so much a town as an eccentric freak of nature. All the winds and airs of heaven play and rush around her walls in summer and in winter. The sun beats down upon her roofs; one seems to see more stars at night, above her ramparts, than one sees in any other town one knows of. All Umbria is spread like a great pageant at her feet, and the pageant is never one day or one hour like the other. Even in a downpour, even in a tempest the great view fascinates. In spring the land is green with corn and oak trees, and pink with the pink of sainfoin flowers. In winter it seems smaller, nearer; brown and gold, and very grand at sundown. On clear days one can easily trace a whole circle of Umbrian cities from the Umbrian capital. To the east Assisi, Spello, Foligno, Montefalco, and Trevi. The hill above Bettona hides the town of Spoleto, but its ilex woods and its convent of Monte Luco are distinct enough. To the south Todi and Deruta stand out clear upon their hillsides; and to the east the home of Perugino, Città della Pieve, rises half hidden in its oakwoods. Early in the mornings you will see the mists lift slowly from the Tiber; at night the moon will glisten on its waters, drawing your fancy down to Rome. Strange lights shine upon the clouds behind the ridge which covers Trasimene, and to the north the brown hills rise and swell, fold upon fold, to meet the Apennines. In autumn and in winter the basin of the old Umbrian lake will often fill for days with mists, but the Umbrian towns and hamlets rise like the birds above them, and one may live in one of these in splendid sunshine, whilst looking down upon a sea of fog which darkens all the people of the plain. The inhabitants of Perugia swear by the healthy nature of their air, and indeed, were it not for the winds, the most fragile constitution would probably flourish in the high hill city. But it must be confessed that there come days when man and horse quiver like dead leaves before the tempest, and when the very houses seem to rock. Indeed, it would be almost impossible to exaggerate the arctic power of a Perugian whirlwind. Yet the average temperature is mild, and myrtles grow to the size of considerable trees in the villa gardens round the town.