Continental trade, as we have seen, had perished with the Roman Empire. Commerce had fallen to its lowest point. There was scarcely any money, nor in any country, neither England, nor France, nor Germany, a native class of merchants; wandering Jews and Greeks and Syrians, and later Italians, carried on what little buying and selling still survived. On the shores of the North Sea, however, the Frisians had made their town of Duurstede, near the mouth of the Rhine, a centre for traffic carried down the river; and in their stout, flat-bottomed, high-boarded sailing ships traded across the North Sea and the Baltic. Duurstede became for a time the chief port of western Europe. There Charles the Great coined money, and the lines along which the Frisian traders carried their wares may still be traced by the finding of the Duurstede coins. But even in the time of the Emperor Charles came the change which was to sweep away the Frisian traders. This was the rise of the new lords of the sea--the Scandinavians--who were to wrest commerce from Frisians and Gauls, and open a new trade for northern Europe. The Scandinavians got their training in a hard school. They had a thousand miles of stormy shores to practice seamanship, fishing along their mountain coasts, and sailing against Arctic tempests round the North Cape. They had to build better ships than anyone else, and to sail them better. They invented a new kind of vessel where both oars and sails were used. And in a short time the Frisians were outdone both in seamanship and in trade.