THE level plains and steppes of South Russia were known to the ancients as the broad channel followed by the ebb and flow of every fresh wave of conquest or migration passing between Europe and Asia. The legions of Rome and Byzance found this territory as impossible to occupy by military force as the high seas... From these refugees and their descriptions of the enemy the sovereigns of Christendom learned with horror of the fate which in the short space of a few months had overtaken the most powerful strongholds of the princes of Rus and Muscovy. Even the Poles – whose more civilized and warlike state was generally considered the bulwark separating the “barbarians” of ancient Scythia from the communities of Europe – had been forced to make the best terms possible: by paying a degrading tribute to the invaders. The powers of Europe now beheld upon the frontiers of their own empires an enemy far more redoubtable than the Saracen “infidels” against whom they had waged their mystical crusades. Turning from his dream of rescuing the Holy Sepulchre the Emperor Frederick II exercised all his eloquence to unite the Christian princes in a league against the Mongols. The Roman Pontiff, fearing for the Christian religion, preached a Holy War. Saint Louis prepared to march in person against the barbarians...