"Although time was running out for horse-borne warriors, they remained formidable in the right circumstances. In the thirteenth century Genghis Khan welded quarrelling Mongol tribes together into a highly centralised state which proved, for a time, to be an unstoppable military force, sweeping away regimes in China and Persia. Mongol warriors were highly mobile and, when they were challenged by forces from more settled empires, withdrew into the vast spaces of Central Asia. One of the secrets of their success may have been another simple piece of technology like the stirrup. Mongol warriors wore silk undershirts, so that if they were hit by an arrow the silk wrapped around its head. It was not only easier to get the arrow out; the risk of infection, until the modern age a greater killer of soldiers than death in battle, was much less. Under Genghis’s successors his warriors stormed westwards through Central Asia and Russia to the shores of the Black Sea, carrying all before them and leaving a trail of death and ruin. No force could stand against them and by 1241 they were probing into Hungary, Poland and present-day Romania and Austria. It looked as though much of what was a weak and divided Europe would become part of their empire – and think what a different history it would have had – when the Mongols suddenly stopped and withdrew in 1242. It may be because word had come that, thousands of miles to the east, the Great Khan had died, but historians have recently speculated that poor weather had turned the ground marshy and ruined the fodder for the Mongol horses."