For migrating, warring and trading humanity therefore, the interest of the mountains is centered in the passes. These are only dents or depressions in the great up-lifted crest, or gaps carved out by streams, or deeper breaches in the mountain wall; but they point the easiest pathway to the ultramontane country, and for this reason focus upon themselves the travel that would cut across the grain of the earth's wrinkled crust. Their influence reaches far. The Brenner, by its medieval trade, made the commercial greatness of Augsburg, Ratisbon, Nuremberg, and Leipzig to the north, and promoted the growth of Venice to the south. The Khaibar Pass and the Gates of Herat in Afghanistan have for long periods dominated the Asiatic policy of Russia and British India. The Mohawk depression and Cumberland Gap for decades gave direction to the streams of population moving westward into the Mississippi basin in the early history of the Republic. Where Truckee Pass (7017 feet) makes a gash in the high ridge of the Sierra Nevada, the California Trail in 1844 sought the line of least resistance across the barrier mass, and deposited its desert-worn immigrants about the Sacramento Valley and San Francisco Bay. There they made a nucleus of American population in Mexican California, and in 1846 became the center of American revolt.
Persistent influence of passes.
Though modern engineering skill, especially when backed by a political policy, may cause certain passes to gain in historical importance at the cost of others, the rule holds that passes are never quite insignificant. Their influence is persistent through the ages. They are nature-made thoroughfares, traversed now by undisciplined hordes of migrating barbarians, now by organized armies, now by the woolly flocks and guardian dogs of the nomad shepherd, now by the sumpter mule of the itinerant merchant, now by the wagon-trains of over-mountain settlers, now by the steam engine panting up the steep grade. Nowhere does history repeat itself so monotonously, yet so interestingly as in these mountain gates. In the Pass of Roncesvalles, notching the western Pyrenees between Pamplona in Spain and St. Etienne in France, fell the army of Charlemagne surprised and beset by the mountain tribes in 778;[1233] through this breach the Black Prince in 1367 led his troops to the victory of Navarette; in the Peninsular War a division of Wellington's army in 1813 moved northward up this valley, driving the French before them; and by this route Soult advanced southward across the frontier for the relief of the French forces shut up in Pamplona. The history of Palestine may be read in epitome in the annals of the Vale of Jezreel, where the highlands of Palestine sink to a natural trough before rising again to the hill country of Galilee and the mountain range of high Lebanon. This was the avenue for war and trade between the Nile and Euphrates, between Africa and Asia. Here the Canaanites expanded eastward from the coast, cutting off northern Israel in Galilee from Samaria and Judea. Here Gideon turned back the incursions of the Midianites or western Arabs. Here was the open road for Assyrians, Egyptians, for Greek armies under Antiochus, and Roman armies under Pompey, Mark Antony, Vespasian and Titus. Hither came the Saracens from the east in 634 A. D. to rout the Greek army, and later the Crusaders from the west, to secure with castle and fortress this key to the Holy Land. Finally, hither came Napoleon from Egypt in 1799 on his way to the Euphrates.[1234]
Geographic factors in the historical importance of passes.
The historical importance of passes tends to increase with the depth of the depression, since the lowest gap in a range relegates the others to only occasional or local use; and with their rarity, in consequence of which intercourse between opposite slopes is concentrated upon one or two defiles. The low dips of the Central American Cordilleras to 262 feet (80 meters) at Panama, 151 feet (46 meters) in the Nicaraguan isthmus, and 689 feet (210 meters) at Tehuantepec, present a striking contrast both orographically and historically to the South American Andes, where from the equator to the Uspallata or Bermejo Pass (12,562 feet or 3842 meters) back of Valparaiso, a stretch measuring 33 degrees of latitude, the passes all reach or exceed 10,000 feet or 3000 meters. The southern or Pennine range of the Alps, stretching as a snow-wrapped barrier from Mont Blanc 90 miles to the central Alpine dome of the St. Gotthard, is notched only by the Great St. Bernard and Simplon passes, which have therefore figured conspicuously in war and trade, since very early times. The Pass of Thermopylæ, as the only route southward along the flank of the Pindus system, figures in every land invasion of Greece from Xerxes to the Greek war of independence. All movements back and forth across the Caucasus wall have been confined to the Pass of Dariel and the far lower Pass of Derbent, or Pylæ Albaniæ; of the ancients, which lies between the Caspian and the last low spurs of the mountains as they drop down to the sea. The latter, as the easier of the two passes, has had a longer and richer history. It alone enabled the ancient Persians temporarily to force a wedge of conquest to the northern foot of the Caucasus, and it has been in all ages a highway for peoples entering Persia and Georgia from the north. It has so far been the only practicable route for a railway from the Russian steppes to the southern base of the Caucasus. While Vladicaucas and Tiflis have direct connection by the military highway over the Pass of Dariel, the railroad between these two points makes a detour of 300 miles to the east.
Intermarine mountains.
Intermarine mountains as a rule offer the easiest passways where they sink to meet the flanking seas. The Pyrenees are crossed by only two railroads, the Bayonne-Burgos line, along the shore of the Bay of Biscay, and the Narbonne-Barcelona line, overlooking the Mediterranean. Between these extremities the passes are very high and only two are practicable for carriages, the Col de la Perche (5280 feet or 1610 meters) between the valleys of the Tet and the upper Segre, and the Port de Canfranc (7502 feet or 2288 meters) on the old Roman road from Saragossa to Oloron. The coastal road around the eastern end of the Cheviot Hills has been the great intermediary between England and Scotland. It was the avenue for early Teutonic expansion into the Scotch Lowlands, the thoroughfare for all those armies which for centuries made Berwick a chronic battleground.