In the mean time the other countries contiguous to the North and Baltic seas, that is, Russia, Sweden, Norway, Denmark, and England, had become converted to Christianity. Some of them, indeed, had embraced the Christian creed several centuries prior to this time. The natural consequence was that a lively intercourse was cultivated upon the two seas, especially after the crusades, which enterprises, by opening new avenues of commerce and increasing the knowledge concerning numerous articles of utility, had greatly augmented the demands of the people of the Occident. The extraordinary development of trade on the Baltic, indeed, vividly recalls the ancient commercial activity on the Mediterranean; and the phrase, "a basin fruitful of culture," often applied to the latter region, may with equal justice be applied also to the former. In the beginning, Russians, Danes, and Englishmen participated in the active trade conducted on the northern littoral. Eventually, however, they were displaced by their German rivals. As the northern nations upon their acceptance of Christianity had once before formed their political and social institutions upon German models, so they now, in such cities as Stockholm, Bergen, Copenhagen, and others, became subject to the cultural and, above all, the commercial influence of the German burgher. It is interesting to note the manner in which this extraordinary influence was secured. In later mediæval times all classes of the population were compelled to rely upon self-help. In other words, they were compelled to replace the defective or insufficient protection afforded by the State by corporate bodies. Thus the merchants of a Low-German German town, when in search of a common centre of trade, pledged themselves by a solemn oath to a defensive and offensive alliance and mutual furtherance; and wider alliances between the various towns themselves soon followed. Of all these private commercial associations none attained to greater importance than did the Gothland Company, a society of Low-German merchants who visited Gothland, the centre of commercial activity in the Baltic, for trading purposes. Here was the seat of the mighty city of Wisby, which contained such wealth that a Danish king once declared that the swine there ate from silver troughs. Even at the present day the massive ruins of the old city wall and of the eighteen churches which once existed there bear testimony to the former magnitude and grandeur of the city. The Gothland Company flourished chiefly during the thirteenth century and enjoyed all the privileges of a political power; bearing its own seal, policing the seas, and insisting upon strict compliance on the part of all navigators of the Baltic with the marine laws which it had created.