Where mountains fail to check, they deflect the historical movement.  The wall of the Carpathians, bulwark of Central Europe, split the westward moving Slav hordes in the 6th century, diverting one southward up the Danube Valley to the Eastern Alps, and turning one northward along the German lowlands.[1211] The northward expansion of the Romans, rebuffed by the high double wall of the Central Alps, was bent to the westward over the Maritime, Cottine and Savoy Alps, where the barrier offered the shortest and easiest transmontane routes.  Hence Germany received the elements of Mediterranean culture indirectly through Gaul, second-hand and late.  The ancient Helvetians, moving southward from northern Switzerland into Gaul, took a route skirting the western base of the Alps by the gap at Geneva, and thus threatened Roman Provincia.  Caesar’s campaigns into northern Gaul were given direction by the massive Central Plateau of France.[1212] The rugged and infertile area of the Catskills long retarded the westward movement in colonial New York and deflected it northward through the Mohawk depression, which therefore had its long thin line of settlements when the neighboring Catskills were still a “bare spot.”

[Sidenote:  Significance of mountain valleys.]

In their valleys, mountains lose something of their barrier nature, and approximate the level of the plains.  Here they harbor oases of denser population and easier intercourse.  Valleys favor human settlement through the milder climate of their lower elevation, the accumulation of soil on their floors, their sheltered environment, and their command of such routes of communication as the highlands afford.  They are the avenues into and within a mountain system, and therefore radically influence its history by their direction and location.  The Central Plateau of France, through the valleys of the Alliers and upper Loire, is most accessible from the north; therefore in that direction it has maintained its most important historical connections,[1213] from the days of Caesar and Vercingetorix.  The massive highland region of Transylvania, which opens long accessible valleys westward toward the plains of the Theiss and Danube, has since the eleventh century received thence Hungarian immigration and political dominion.[1214] Its dominant Roumanian population, however, seems to have fled thither from the Tartar-swept plains to the southeast.

The anthropo-geography of mountain valleys depends upon the structure of the highlands themselves, whether they are fold mountains, whose ranges wall in longitudinal valleys, or dissected plateaus, whose valleys are mostly transverse river channels leading from the hydrographic center out to the rim of the highlands.  Longitudinal valleys are not only long, but also broad as a rule and often show a nearly level floor.[1215] They therefore form districts of considerable size, fertility, and individuality, and play distinct historical roles in