But such boats were adapted only to the comparatively calm and simple navigation of the Mediterranean; and although imitated in the similar waters of the eastern Baltic, they never flourished north of Spain. When they gradually disappeared, their successor inside the gates of Gibraltar was the xebec, which began to appear under Arab or Spanish control in the seventeenth century; this was supposed to be able to withstand any weather, and carried from fourteen to twenty-two guns on deck, with small ports for oars between the guns. A picturesque relative was the Portuguese muleta. The English liked this kind of vessel on account of its strong sailing qualities, but when they took it into their own stormy waters they found it necessary to raise its sides to fit them for breasting the high seas that roll in the open Atlantic or are tossed by the contending tides of the English Channel, and developed out of it a style of swift and handy vessel called a frigate. During all these “middle” ages the northern nations had been sailing and fighting on the sea as well as the southerners. Stories of sturdy battles have come down in tradition and in such chronicles as those of Froissart; but those old conflicts seem to have produced little change in ship-building or armament until the experience and wisdom brought back by the Crusaders began to spread abroad even in the half-savage North, and to produce that revival of learning which by and by was to make such striking changes in western Europe; and here the leaders are Englishmen. [Illustration: FORECASTLE OF THE “GREAT HARRY” (“GRÂCE DE DIEU”).]