Their extraordinary voyages were made in boats that resemble so closely Greek and Roman models--even Phoenician, for that matter--as to suggest that the Vikings learned their ship-building from Mediterranean traders who forced their way into the Baltic in very early times. For example, the Viking method of making a rib in three parts is identical with the method of the Greeks and Romans. The chief points of difference are that Viking ships were sharp at both ends--like a canoe, were round-bottomed instead of flat, and had one steering oar instead of two. The typical Viking ship was only about 75 feet in length; but a royal vessel--the _Dragon_ of the chief--sometimes attained a length of 300 feet, with sixty pairs of oars. If the Vikings had had national organization under one head, they might well have laid the rest of Europe under tribute. In the 11th century, Cnut, a descendant of the Vikings, ruled in person over England, Denmark, and Norway. But their ocean folk-wanderings seem to have ended as suddenly as they began, and the effects were social rather than political. Where they settled, they brought a strain of the hardiest racial stock in Europe to blend with that of the conquered peoples. _The Hanseatic League_ During the Middle Ages, peaceful trading gradually gained the upper hand over piracy and conquest. From the Italian cities the wares of the south and the Orient came over the passes of the Alps and down the German rivers, where trading cities grew up to act as carriers of merchandise and civilization among the nations of the north. The merchant guilds of these cities, banded together in the Hanseatic League, for at least three centuries dominated the northern seas. Perhaps the most extensive commercial combination ever formed for the control of sea trade, the Hanseatic League began with a treaty between Luebeck and Hamburg in 1174, and at the height of its power in the 14th and 15th centuries it included from 60 to 80 cities, of which Luebeck, Cologne, Brunswick, and Danzig were among the chief. The league cleared northern waters of pirates, and used embargo and naval power to subdue rivals and promote trade. It established factories or trading stations from Nishni Novgorod to Bergen, London, and Bruges. From Russia it took cargoes of fats, tallows, wax, and wares brought into Russian markets from the east; from Scandinavia, iron and copper; from England, hides and wool; from Germany, fish, grain, beer, and manufactured goods of all kinds. The British pound sterling (Oesterling) and pound avoirdupois, in fact the whole British system of weights and coinage, are legacies from the German merchants who once had their headquarters in the Steelyard, London.