the market of the Punjab by a circuitous route through the Hajikhak Pass (12,188 feet) or famous Gates of Bamian over the main range of the Hindu Kush, by the Unai Pass over the Paghman Mountains to Kabul at 5740 feet, and then by gorges of the Kabul River and the Khaibar Pass (6825 feet) down to Peshawar.  This road presents so many difficulties that caravans from Turkestan to India prefer another route from Merv up the valley of the Heri-Rud through the western hills of the Hindu Kush to Herat, thence diagonally southeast across Afghanistan to Kandahar, and thence by the Bolan Pass down to the Sind.  The broad, low series of forested mountains consisting of the Vindhyan and Kaimur Hills, reinforced by the Satpura, Kalabet, Gawilgarh ranges, Mahadeo Hills, Maikal Range and Chutia Nagpur Plateau as a secondary ridge to the south, forms a double barrier across the base of peninsular India.  It divides the Deccan from Hindustan so effectually that it has sufficed to set limits to any Aryan advance en masse southward.  It kept southern India isolated, and admitted only later Aryan influences which filtered through the barrier.  To people accustomed to treeless plains, these wide belts of wooded hills were barrier enough.  Even a few years ago their passes were dreaded by cartmen; most of the carriage of the country was effected by pack-bullocks.  Even when roads were cleared through the forests, they were likely to be rendered impassable by torrential rains.[1223]

[Sidenote:  Dominant trans-montane routes.]

Where a broad, complex mountain system contracts to narrow compass, or is cut by deep reentrant valleys leading up to a single pass, the transmontane route here made by nature assumes great historical Importance.  The double chain of the mighty Caucasus, from 120 to 150 miles wide and 750 miles long, stretches an almost insuperable barrier between the Black Sea and the Caspian.  But nearly midway between these two seas it is constricted to only 60 miles by a geographical and geological gulf, which penetrates from the steppes of Russia almost to the heart of the system.[1224] This gulf forms the high valley of the Terek River, beyond whose headstream lies the Dariel defile (7503 feet or 2379 meters), which continues the natural depression across to the short southern slope.  All the other passes of the Caucasus are 3000 meters or more high, lie above snow line and are therefore open only in summer.  The Dariel Pass alone is open all the year around.[1225] Here runs the great military road from Vladicaucas to Tiflis, which the Russians have built to control their turbulent mountaineer subjects; and here are located the Ossetes, the only people among the variegated tribes of the whole Caucasus who occupy both slopes.  All the other tribes and languages are confined to one side or the other.[1226] Moreover, the Ossetes, occupying an exposed location in their highway habitat, lack the courage of the other mountaineers, and yielded without resistance to the Russians.  In this respect they resemble the craven-spirited Kashmiri, whose mountain-walled vale forms a passway from Central Asia down to the Punjab.