First Swedish Crusade

The earliest written sources of the crusade are from the late 13th century. The main sources of the crusade, the legend of Saint Erik and the legend of Saint Henry, describe the crusade as caused by the multiple raids of pagan Finns on Sweden.

The crusade has traditionally been seen as the beginning of Swedish rule over Finland and the first attempt of the Catholic Church and Sweden to convert Finnish pagans to Christianity. However, the Christianisation of Southwestern Finland is known to have already started in the 10th century, and in the 12th century, the area was probably almost entirely Christian. According to legends, after the crusade, Bishop Henry was killed at Lake Köyliö by Lalli. Henry later became a central figure of the Catholic Church in Finland.

Veracity of the crusade

Academics debate whether this crusade actually took place. No archaeological data gives any support for it, and the earliest written sources are from much later. No surviving written source describes Finland under Swedish rule before the end of the 1240s. Furthermore, the diocese and the bishop of Finland are not listed among their Swedish counterparts before the 1250s. Also, the Christianisation of south-western Finland is known to have already started in the 10th century, and in the 12th century, the area was probably almost entirely Christian. It is possible that the Swedish bishop who had authority over Finland's bishop was the bishop of Linköping, not the bishop of Uppsala.

The First Novgorod Chronicle relates that in 1142, a Swedish prince and bishop, accompanied by a fleet of 60 ships, attacked Russian tradesmen; the circumstances are unclear, but indicate that Sweden and the Novgorod Republic were engaged in a struggle for the northern trade routes.