Sluys is often spoken of as the sea-fight that inaugurated the long victorious career of the British Navy. It would be more correct to say that it was the battle which, by giving King Edward the command of the Channel, made his successful invasion of France possible, and secured for England the possession of Calais. Holding both Dover and Calais the English for two centuries were masters of the narrow sea-gate through which all the trade between northern Europe and the rest of the world had to pass. They had the power of bringing severe pressure to bear upon the German cities of the Hansa League, the traders of the Low Countries, the merchants of Spain, Genoa, and Venice, by their control of this all-important waterway. Hence the claim upheld till the seventeenth century that the King of England was "Sovereign of the Seas," and that in the Channel and the North Sea every foreign ship had to lower her sails and salute any English "King's ship" that she met. Sluys, which had such far-reaching consequences, was not the first of English naval victories. Alfred the Great maintained in the latter part of his reign a fleet of small ships to guard the coasts against the Norse and Danish pirates, and this won him the name of founder of the British Navy. But for centuries after there was no attempt at forming or keeping up a regular naval establishment. Alfred's navy must have been dispersed under his weaker successors, for the Northmen never found any serious obstacles to their raids. Harold had no navy, and the result was that in a single twelvemonth England was twice invaded, first by Harold Hadrada and Tostig, who were beaten at Stamford Bridge, and then by William the Norman, who conquered at Hastings. But even the Conqueror had no fighting fleet. His ships were used merely to ferry his army across the Channel, and he made no attempt to use them against the Northmen who harried the east coast. The record of victory begins with the reign of King John, when in 1213 William Longsword, his half-brother, with a fleet gathered from the shipping of Dover and the south-eastern ports, destroyed a French fleet that had assembled on the coast of the Netherlands to transport an invading army to England. Damme (i.e. "the dams or embankments to keep out the sea") was then a fortified port. It is now a Dutch village, some miles from the coast, in the midst of green meadows won from the sea, with roads shaded by avenues of trees, and only the traffic of its canal to remind it that it once had a harbour.