THE GEOGRAPHIC BASIS • OF HISTORY 383
meteorological records show that the rainfall at certain Siberian stations near the centre of Asia may vary in the ratio of two and three tenths in the good years to one in the bad years. Therefore we can scarcely be exaggerating if we assume that during the great and relatively sudden desiccation in the early part of our era, the average rainfall decreased in the ratio of two to one. If it fell from thirteen inches to six or seven, the nomads would have been able to find pasture for only one sheep where formerly they found it for fifteen. If the rainfall fell from twenty inches to ten, the number of sheep would decrease from sixty to one. Manifestly, if such a change took place in the course of a few hundred years, most of the inhabitants would be obliged to migrate. As the nomads pressed outward from the drier central regions of Asia, we can imagine how they were obliged to fight with the neighboring tribes whom they tried to dispossess. The old inhabitants and the newcomers could not all live together; new migrations would be a necessity; and confusion would spread in every direction. Meanwhile, Europe, after its long period of blighting cold, was becoming warm and habitable, and the migrants pressed into it, horde after horde. No one tribe could stay long in its chosen abiding-place, for new bands of restless nomads pressed upon it. Rome fell before the wanderers. Nothing could stay their progress until the turn of the tide.
Perchance, though this is only vague conjecture, the legends of King Arthur and his knights bear a hint of what might have occurred all over Central Europe if it had not been for the influx of barbarians. England, in its remote corner of Europe, far from the dry plains of Asia, responded
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