The siege of Caffa, and the general circumstances of it, we may take as historical on the authority of the Italian notary who was there; but it may be doubted whether the plague began, as he says, among the nomade hordes outside the fort. In sieges it has been not unusual for both sides to suffer from infective disease; and although it is not always easy to say where the disease may have begun, the presumption is that it arose among those who were most crowded, most pressed by want, and most desponding in spirit. It is, of course, not altogether inconceivable that the Tartar besiegers of Caffa had bred a pestilential disease in their camp; the nomades of the Cyrenaic plateau have bred bubo-plague itself more than once in recent years in their wretched summer tents, and plague has appeared from time to time in isolated or remote Bedouin villages on the basaltic plateaus of Arabia. There is nothing in the nomade manner of life adverse to pestilential products, least of all in the life of nomades encamped for a season. But such outbreaks of bubo-plague or of typhus fever have been local, sporadic, or non-diffusive. On the other hand the plague which arose at the siege of Caffa was the Black Death, one of the two greatest pestilences in the history of the world. Let us then see whether there is any greater likelihood of finding inside the walls of Caffa the lurking germs of so great a pestilence. Within the walls of the Genoese trading fort were the Italian merchants driven in from all around that region, with their merchandise--as De Mussis says, _fugientes pro suarum tutione personarum et rerum_. Previous to their three years’ siege in Caffa they, or some of them, had stood a siege in Tana, and had retreated to the next post on the homeward route. Tana was at the eastward bend of the Don, whence the road across the steppe is shortest to the westward bend of the Volga; a little above the bend of the Volga was the great city of Sarai--whence the caravans started on their overland journey along northern parallels, across mountain ranges and the desert of Gobi, to enter China at its north-western angle, just within the end of the Great Wall[289]. The merchandise of Sarai and Tana was the return merchandise of China--the bales of silks and fine cloths, spices and drugs, which had become the articles of a great commerce between China and Europe since Marco Polo first showed the way, and which continued to reach Europe by the caravan routes until about 1360: then the route was closed owing to the final overthrow of the authority of the Great Khan, which had once secured a peaceful transit from the Yellow Sea to the Black Sea--so completely closed that men forgot, two hundred years after, that it had ever existed.