We are also driven to the conclusion that other nations, capable of conducting extensive mining operations, must have been in existence in the Caucasus, the Hindoo-Kush, the Altai, or other remote regions; and that routes of international commerce must have been established by which the scarce but indispensable tin could be transported from these regions to the dense and civilized communities which had grown up in the alluvial valleys and deltas of the Nile and the Euphrates. It is very singular, however, that if such an intercourse existed, the knowledge of other objects of what may be called the first necessity, should have been so long limited to certain areas and races. For instance, in the case of the domestic animals, the horse was unknown in Egypt and Arabia till after the Hyksos conquest, when in a short time it became common, and these countries supplied the finest breeds and the greatest number of horses for exportation. On the other hand, the horse must have been known at a very early period in Chaldæa, for the tablet of Sargon I., B.C. 3800, talks of riding in brazen chariots over rugged mountains. This makes it the more singular that the horse should have remained so long unknown in Egypt and Arabia, for it is such an eminently useful animal, both for peace and war, that one would think it must have been introduced almost from the very first moment when trading caravans arrived. And yet tin must have arrived from regions where in all probability the horse had been long domesticated before the time of Menes. The only explanation I can see is, that the tin must have come by sea, but by what maritime route could it have come prior to the rise of Phoenician commerce, which was certainly not earlier than about 2000 B.C., or some 3000 years after the date of Menes? Could it have come down the Euphrates or Tigris and been exported from the great sea-ports of Eridhu or Ur by way of the Persian Gulf and Red Sea?