[Sidenote:  Contrasted accessibility of opposite slopes.]

Mountains are seldom equally accessible from all sides.  Rarely does the crest of a system divide it symmetrically.  This means a steep, difficult approach to the summit from one direction, and a longer, more gradual, and hence easier ascent from the other.  It means also in general a wide zone of habitation and food supply on the gentler slope, a better commissary and transport base whence to make the final ascent, whether in conquest, trade or ethnic growth.  Mountain boundaries are therefore rarely by nature impartial.  They do not umpire the great game of expansion fairly.  They lower the bars to the advancing people on one side, and hold them relentlessly in place to the other.  To the favored slope they give the strategic advantage of a swift and sudden descent beyond the summit down the opposite side.  The political boundary of France along the watershed of the Vosges Mountains is backed by a long, gradual ascent from the Seine lowland and faces a sharp drop to the rift valley of the middle Rhine, Its boundary along the crest of the Alps from Mont Blanc to the Mediterranean brings over two-thirds of the upheaved area within the domain of France, and gives to that country great advantages of approach to the Alpine passes at the expense of Italy.  With the exception of the ill-matched conflict between the civilized Romans and the barbarian Gauls, it is a matter of history that from the days of Hannibal to Napoleon III, the campaigns over the Alps from the north have succeeded, while those from the steep-rimmed Po Valley have miscarried.  The Brenner route favored alike the Cimbri hordes in 102 B.C. and later the medieval German Emperors invading Italy from the upper Danube.  The drop from the Brenner Pass to Munich is 2800 feet; to Rovereto, an equally distant point on the Italian side, the road descends 3770 feet.

[Sidenote:  Its ethnic effects.]

The inequality of slope has ethnic as well as political effects, especially where a latitudinal direction also makes a sharp contrast of climate on the two sides of the mountain system.  Except in the Roman period, the southern face of the Alps has been an enclosing wall to the Italians.  The southern cultivator penetrated its high but sunny valleys only when forced by poverty, while the harsh climate on the long northern slope effectively repelled him.  On the other hand, Switzerland has overstepped the Alpine crest in the province of Ticino and thrust its political boundary in a long wedge down to the lowland of the Po near Como; and the Alpine race, spilling everywhere over the mountain rim into the inviting Po basin, has given to this lowland population a relatively broad skull, blond coloring and tall figure, sharply contrasted with the pure Mediterranean race beyond the crest of the Apennines.[1229]