The little cities on the coast of north-western Europe had an interesting story of their own. The mediaeval world ate a great deal of fish. There were many fast days and then people were not permitted to eat meat. For those who lived away from the coast and from the rivers, this meant a diet of eggs or nothing at all. But early in the thirteenth century a Dutch fisherman had discovered a way of curing herring, so that it could be transported to distant points. The herring fisheries of the North Sea then became of great importance. But some time during the thirteenth century, this useful little fish (for reasons of its own) moved from the North Sea to the Baltic and the cities of that inland sea began to make money. All the world now sailed to the Baltic to catch herring and as that fish could only be caught during a few months each year (the rest of the time it spends in deep water, raising large families of little herrings) the ships would have been idle during the rest of the time unless they had found another occupation. They were then used to carry the wheat of northern and central Russia to southern and western Europe. On the return voyage they brought spices and silks and carpets and Oriental rugs from Venice and Genoa to Bruges and Hamburg and Bremen. Out of such simple beginnings there developed an important system of international trade which reached from the manufacturing cities of Bruges and Ghent (where the almighty guilds fought pitched battles with the kings of France and England and established a labour tyranny which completely ruined both the employers and the workmen) to the Republic of Novgorod in northern Russia, which was a mighty city until Tsar Ivan, who distrusted all merchants, took the town and killed sixty thousand people in less than a month's time and reduced the survivors to beggary. That they might protect themselves against pirates and excessive tolls and annoying legislation, the merchants of the north founded a protective league which was called the "Hansa." The Hansa, which had its headquarters in Lubeck, was a voluntary association of more than one hundred cities. The association maintained a navy of its own which patrolled the seas and fought and defeated the Kings of England and Denmark when they dared to interfere with the rights and the privileges of the mighty Hanseatic merchants. I wish that I had more space to tell you some of the wonderful stories of this strange commerce which was carried on across the high mountains and across the deep seas amidst such dangers that every voyage became a glorious adventure. But it would take several volumes and it cannot be done here. Besides, I hope that I have told you enough about the Middle Ages to make you curious to read more in the excellent books of which I shall give you a list at the end of this volume.