Foes though they were in name, there was always a certain amount of friendly intercourse between the Crusaders and the Saracens, and the former were bound to be affected in some degree by the civilisation of the latter. Sometimes a dark-faced "leech" would return in the train of a Crusading baron to Europe, and there would teach some of his mysteries of healing to the rough-and-ready doctors of the West. To the Arabs we owe our "Arabic" system of numbers, used instead of the clumsy Roman figures, and the knowledge of the decimal notation, by which nearly every civilised country except our own reckons its money. From Architecture to Geography, all those branches of knowledge which distinguish the educated from the uneducated mind, may be traced back to the keen and subtle intelligence of the East. Next perhaps in importance comes the opening up of the East to the West for purposes of Commerce. Many a knightly Crusader thought it no shame to carry on an extensive trade in the silks and spices of Palestine in order to fill his coffers upon his return and that he might be recompensed for the expenses of his undertaking. The constant crossing and recrossing of the Mediterranean soon set on foot a steady stream of commercial enterprise between the seaports of Italy and those of Syria, and the existence of a Latin Empire of Constantinople impelled Venice, the main cause of its establishment, to still closer communication with the East. To her, as "the Southern terminus of a great land trade-route," was carried the produce of England, {279} Norway, Flanders, France and Germany as to a huge market, and she distributed it throughout the Eastern world, receiving in return the wealth of the latter to be carried back to Europe. It was only when the discovery of America opened up an entirely new field of enterprise that this great stream of commerce began to diminish. Another effect of the Crusades was upon the great world of literature. Such a unique event as a Holy War was bound to inspire the writers of history even in the days when such writers were rarely to be found. William of Tyre was only one amongst several chroniclers of the First Crusade, and the story of the Crusades of later days have been vividly told by Richard of Devizes, Villehardouin and the Sire de Joinville, many of whose telling descriptions have been quoted in the pages of this book. It was but natural that the gallant adventures of the Crusaders should form the theme of many of the epics and _chansons_ of Chivalry. Charlemagne, Roland and Bevis of Hampton may never have seen the Holy Land, but they became the heroes of Crusading exploits nevertheless; while Richard Lion-Heart and Godfrey of Boulogne, actual leaders in the Holy War, became the central figures of more or less impossible legendary adventures.