In 1229 Finland Christianity, Traditional Religions Pope Gregory IX authorizes Bishop Thomas, the first Christian bishop of Finland, to assume control over all non-Christian places of worship throughout Finland. Shortly thereafter, the Tavastians, a subgroup of the Finnish people, rebel against Christianity, which prompts the pope to call for a crusade specifically against them.
The victory of the Christian faith and the ecclesiastical order marked the end of prehistory in Finland and the beginning of the Middle Ages.
In the 1150s, Erik, king of Sweden, and Henrik, bishop of Uppsala, tried to introduce ecclesiastical and political order in Finland (the so-called “first crusade”). Sweden was not able to subjugate Finland, but missionary work and establishment of the first parishes were initiated in Lower Satakunta and the northern part of Varsinais-Suomi. The missions under the leadership of bishops, and perhaps also the crusades waged by the Swedish aristocracy, continued in Finland all through the latter half of the 12th century. Ecclesiastical order was also established in spite of the harassment of Novgorod and paganism.
Because of the conquests by the Germans and the Danes in the Baltic countries, Sweden also launched her operations in the coastal countries of the Gulf of Finland at the beginning of the 13th century. They had been initiated mainly in the dioceses of Gotland and Linkoping. From about 1220-1245, the bishop of Finland was the energetic Thomas; and as a result of his efforts, the diocese of Finland came to comprise the provinces of Varsinais, Suomi and Hame. Thomas sought support particularly from the German rulers in the Baltic countries, and probably also received armed assistance for his operations from the order of the Brethren of the Sword against paganism in Hame and against Novgorod during the 1230s. The diocese of Finland does not seem to have been under the authority of the bishop of Uppsala in his time, although the connection was established soon after Thomas at the end of the 1240s.
The participation of Catholic bishops in military campaigns was the norm rather than the exception in the 13th century. Their participation in these instances does not offer any proof whatsoever of the direct interest of the curia or the pope or that they were directing events.
The young missionary church in Finland seems to have played a more active role in the 1220s than earlier. The first phase of missionary work was over, and now an independent bishopric under the guidance of the archbishop of Uppsala was erected. In 1221, Pope Honorius III gave the Finnish bishop extensive powers of attorney in the territory north of the Finnish gulf (including a trade boycott against the pagan people), in order to make the missionary work among the non-Christians more effective. The papal letters mention an unspecific bishop of Finland. The bishop mentioned was perhaps Bishop Thomas (c. 1230-1245), who appears in sources for the first time in 1232. The boycott of trade was a consequence of Novgorodian attacks to Tavastia; as a result, the Tavastians made raids and caused devastation in Karelia. From the year 1229, seven of Pope Gregory IX’s letters defending the Finnish church have been preserved. One of the letters allows the transfer of the centre of the bishopric from Nousiainen to Koroinen in Turku. The transfer of the episcopal see to a more suitable place meant advantages to the bishopric concerning trade and communication.
Bishop Thomas seems to have been especially active in fighting the non-Christian Finns. When Finland proper in the southwest and the Åland islands had been Christianized for a long time, missionary endeavours were directed towards Tavastia. It seems that Bishop Thomas possibly established contact with the German Sword Brethren in Livonia and managed to convince at least some of the Brethren to help defend Christianity in Tavastia. Whether the Sword Brethren were ever active in Finland is unclear, however. The often brutal methods used to convert the inhabitants of Tavastia, which could indicate the presence of the Sword Brethren, inspired in 1237 a huge riot among the Tavastians against the Swedes and the Swedish ecclesiastical hierarchy. In 1240, Bishop Thomas, other Swedish bishops, and Birger Magnusson participated in the battle of Neva, where Prince Alexander Nevsky of Novgorod soundly defeated his enemies.
The Swedish military expedition against Tavastia is normally thought of as the second Finnish crusade. The events of this military campaign are referred to in the Erik Chronicle (written c. 1331-1332). According to the chronicle, the second crusade was conducted by Earl Birger (Birger Jarl). Although it does not mention any year, it is clear from the context that it must have taken place in 1249, even though Finnish historian Jarl Gallén has argued convincingly for an earlier dating of the crusade to 1238-1239. It is, however, general consensus that the second crusade must have taken place in 1249. This takes into account the fact that Birger Jarl might have ravaged Finland twice – in 1238-1239 and again in 1249-1250 – to install a new bishop on the vacant episcopal see of Turku. The chronicle describes how the Swedish troops led by Birger Jarl successfully traced the Tavastians and defeated them. The Earl then founded and erected the castle of Hämeenlinna in order to strengthen Swedish control over the territory. The place of the first stronghold was perhaps the Haga (Fin. Hakoinen) castle in Janakkala, because an early construction on the later location of the Hämeenlinna castle seems problematic and cannot be documented.
The earlier military undertakings by the Danes with the conquest of Estonia in 1219 might have served as one of the catalysts for the Swedish endeavours to strengthen their military power towards Novgorod. The Novgorodian victory by Neva in 1240, however, did not definitively stop the Swedish expansion policy. The Swedes thus took part in a German attack on Novgorod in 1256 in the area east of the River Neva; Prince Alexander Nevsky attacked Tavastia the following winter.
The Swedish military activities against Tavastia in the 1230s and 1240s strengthened not only the position of the Swedish crown in the territory, but also the position and the prestige of Bishop Thomas. The landscape was Christianized by the Swedes and, according to the Erik Chronicle, the `Russian prince’ lost control of Tavastia. Bishop Thomas was, however, forced to resign in 1245. The actual circumstances around his withdrawal are complicated. Some claim that the military defeat against Alexander Nevsky in 1240 was the reason for his demission; on the other hand, a papal letter reveals that he was found guilty of use of torture and killing, as well as of falsifying papal letters. Bishop Thomas spent the last years of his life in the Dominican convent in Visby in Gotland. The Dominicans were active in helping to convert the pagans, and perhaps an earlier collaboration with members of the newly founded order explains the Bishop’s decision. Bishop Thomas’s personality has always been hotly debated. The bishop’s seat in Turku remained vacant after his dismissal and was filled only in 1248-1249, when Bero, the chancellor of the Swedish king, was appointed.