The story of the commerce of Central Asia, which centred itself in Herat in the days of Arab supremacy, has a strong claim on the student of Eastern geography, for it is only through the itineraries of these wandering Semetic merchants and travellers that we can arrive at any estimation of the peculiar phase of civilization which existed in Asia in the mediæval centuries of our era; a period at which there is good reason to suppose that civilization was as much advanced in the East as in the West. It is not the professional explorers, nor yet the missionaries (great as are their services to geography), who have opened up to us a knowledge of the world's highways and byways sufficient to lead to general map illustration of its ancient continents, so much as the everlasting pushing out of trade investigations in order to obtain the mastery of the road to wealth.
India and its glittering fame has much to answer for, but India (that is to say, the India we know, the peninsula of India) was so much more get-at-able by sea than by land even in the early days of navigation, that we do not learn so much about the passes through the mountains into India as the way of the ships at sea, and the coast ports which they visited. According to certain Arab writers large companies of Arabs settled in the borderland and coasts of India from the very earliest days. Indeed, there are evidences of their existence in Makran long before the days of Alexander; but there is very little evidence of any overland approach to India across the Indus. Hindustan, to the mediæval Arab, commenced at the Hindu Kush, and Kabul and Ghazni were "Indian" frontier towns; and the invasions and conquests of India dating back to Assyrian times include no more than the Indus basin, and were not concerned with anything farther south. The Indus, with its flanking line of waterless desert, was ever a most effectual geographical barrier.
The Arabs entered India and occupied the Indus valley through Makran, and throughout their writings we find, strangely, little reference to any of the Indian frontier passes which we now know so well. But in the north and north-west of Afghanistan, in the Seistan and the Oxus regions, they were thoroughly at home both as traders and travellers; and with the assistance of their records we can make out a very fair idea of the general network of traffic which covered High Asia. The destroying hordes of the subsequent Mongol invasions, and the everlasting raids of Turkmans and Persians on the border, have clean wiped out the greater number of the towns and cities mentioned by them, and the map is now full of comparatively modern Turkish and Persian names which give no indication whatever of ancient occupation. There are, nevertheless, some points of unmistakable identity, and from these we can work round to conclusions which justify us in piecing together the old route-map of Northern Afghanistan to a certain extent. This is not unimportant even to modern geographers. The roads of the old khafila travellers may again be the roads of modern progress. We know, at any rate, that the Arabs of 1000 years ago were much the same as the Arabs of to-day in their manners and methods. Their routes were camel routes, not horse routes, and their day's journey was as far as a camel could go in a day, which was far in the wider and more waterless spaces of desert or uninhabited country, and very much shorter when convenient halting-places occurred. These Arab itineraries are bare enumeration of place-names and approximate distances. As for any description of the nature of the road or the scenery, or any indication of altitude (which they possibly had no means of judging), there is not a trace of it; and the difficulties of transliteration in place-names are so great as to leave identification generally a matter of mere guesswork.