As the Germans had swarmed southward years earlier, so Norsemen from the Scandinavian peninsula made piratical excursions up the French rivers, seized the district in the north afterward called Normandy, and wrested eastern England from the Saxon king, Alfred. Other adventurers pushed southeast from Sweden and into Russia where they founded a royal line in the ninth century. The monk Ansgar went to Denmark and Sweden as a missionary and from his diocesan headquarters at Hamburg, he was apostolic vicar of the pope over all Scandinavia. But the progress of Christianity was slow. In Norway, King Olaf Trigvason was baptized by a hermit, did his best through a short reign to convert his people, and sent missionaries to Iceland and to Greenland. Greenland had a bishop in the tenth century. In the twelfth century, Swedish missionaries went into Finland, and each of the three Scandinavian countries eventually had its own bishop.
Impact: In becoming Christians the Norsemen did not lose all of their adventurous spirits, but they came into peaceful relations with continental Europe. Subsequently, they formed part of the trading system of the Hanseatic League.