It is probable that such decorations were not unfrequently the prizes of piracy rather than of fair trade: for, though some of the people of the southern portions of Norway are said to have been considerable traders to England, Ireland, Saxony, Flanders, and Denmark, yet their attachment to trade in no way interfered with occasional amusements of a very different kind, or with quartering themselves during the winters on the countries of the Christians. Nor were they particular in their objects of plunder. In the periodical fairs of Germany, which were established about this period, a large portion of the merchandise brought to them for sale consisted of slaves of both sexes; ordinary slaves of either sex realizing about a mark, or eight ounces of silver, while three times that sum was frequently given, at these northern fairs, for female slaves who were “fair in form and beautiful in countenance.” Helmold relates that he saw seven thousand Danish slaves at one time exposed for sale in the market at Mecklenburg.[498] [Sidenote: Mode of navigating.] Long before the compass was known, the seamen of Norway, like the ancient mariners of the Island of Ceylon, regulated their track through the ocean by the flight of birds set free from on board their vessels; a proof that, in regions of the world far removed from each other, the same primitive practices prevailed. It is related of Flok,[499] a famous Norwegian navigator, that when about to set out from Shetland[500] to Iceland, he took with him some crows on board of his ship. Under the impression that he had made considerable progress in his voyage, he liberated one of these birds, which, seeing land astern, flew for it; whereby Flok, considering that he was nearer Shetland or Faroe “than any other land, kept on his course for some time, and then sent out another crow, which, seeing no land at all,” returned to the vessel. At last, as he conceived, having accomplished the greatest part of his voyage, a third crow was set at liberty, which seeing land ahead immediately flew for it, and Flok, following his guide, fell in with the east end of the island of Iceland. [Sidenote: Canute, A.D. 1016. Reduction of the English fleet.] [Sidenote: A.D. 1031.]