due to both their participation in commerce and their plundering. There is evidence of possible Viking settlements on the Finnish mainland. The Åland Islands were probably settled from Sweden during the Viking period. During the 11th and 12th centuries, Sweden gradually became a unified Christian kingdom. According to the archaeological finds, Christianity first gained a foothold in Finland during the 11th century as well. Later medieval legends describe Swedish attempts to conquer and 'Christianize' Finland by the First Swedish Crusade sometime in the mid-1150s. In the early 13th century, Bishop Thomas became the first bishop of Finland. There were several secular powers who aimed to bring Finland under their rule but the Swedish regent Birger Jarl established Swedish rule in Finland through the Second Swedish Crusade, which is most often dated at 1249. Middle Ages Finland gradually became an integrated and important part of Sweden. Finland became known as Österland, and its main urban settlement evolved in Åbo. Åbo was one of the biggest towns in the kingdom of Sweden, and its population included German merchants and craftsmen. Otherwise the degree of urbanization was very low in medieval Finland. During the 12th and 13th centuries, great numbers of Swedish settlers moved to the southern and north-western coasts of Finland, including Åland and the archipelago between Åbo and the Åland Islands. In these regions, the Swedish language is widely spoken even today. Swedish came to be the language of the high-status people in many other parts of Finland as well. In 1362, representatives from Finland were called to participate in the elections for king of Sweden. That year is often held to signify the incorporation of Finland into the kingdom of Sweden. As in the Scandinavian part of the kingdom, a gentry or (lower) nobility consisted of magnates and yeomen who could afford armament for a man and a horse. These were concentrated in the southern part of Finland. After the Black Death and internal power struggles in Sweden, Queen Margaret I of Denmark united the Nordic countries in the Union of Kalmar in 1397, with the approval of the Swedish nobility. Finland was sometimes involved in these struggles, but in general the 15th century seems to have been a relatively prosperous time, characterized by population growth and economic development. Towards the end of the 15th century, however, the situation on the eastern border was becoming more tense. The Principality of