In the year A.D. 829, ambassadors from Sweden presented themselves at the court of Louis, and after arranging the political object of their mission, announced that many of their countrymen were favourably disposed towards Christianity. The commerce carried on at this period between Sweden and the port of Doerstadt, combined with the teaching of some Christian captives, whom the Swedes had carried off in their piratical excursions, had predisposed not a few towards lending a favourable ear to Christian teachers. The emperor gladly embraced the opportunity thus afforded, and summoned Anskar to the palace, who, after an interview, declared his entire willingness to undertake the enterprise. A monk named Gislema was therefore left with Harold, and Anaskar having found a new companion in Witmar, a brother monk of Corbey, set out in the year A.D. 831 with presents from Louis to the King of Sweden. But the voyage was most disastrous. The missionaries had not proceeded far when they were attacked by pirates. A fierce battle ensued, and their crew, though first victorious, were overpowered in a second engagement, and barely escaped to land. The pirates plundered them of everything, the presents for the king, their sacred books, and all their ecclesiastical vestments. In this forlorn and destitute condition they reached Birka, a haven and village on the Mälar lake, not far from the ancient capital Sigtuna, the residence of rich merchants, and the centre of the northern trade. Here they were hospitably welcomed by the king, Biorn "of the Hill," and received full permission to preach and baptize. The nucleus of a church was found already existing in the persons of many Christian captives, who had long been deprived of the consolation of Christian ordinances. The work, therefore, of the missionaries commenced under fair auspices, and before long Herigar, the king's counsellor, announced himself a convert, and erected a church on his estate. A year and a half was thus employed, and then Anskar returned to the court of Louis with a letter from the King of Sweden, and an account of all that had befallen him. Thereupon Louis resolved, without delay, to give effect to the ecclesiastical plans of his father, and to make Hamburg an archiepiscopal see, and the centre of operations for the northern missions. Accordingly, Anskar was elevated to the archiepiscopal dignity, and was consecrated at Ingleheim by Drogo, Archbishop of Mayence, and other prelates. At the same time, because of the poverty of the diocese, and the dangers to which the mission would be inevitably exposed, the monastery of Thourout in Flanders, between Bruges and Ypres, was assigned to him as a place of refuge, and a source of revenue. Then he was directed to repair to Rome, where he received the pall from Gregory IV., and was regularly authorized to preach the Gospel to the nations of the North.