Duke of Finland

Duke of Finland (Finnish: Suomen herttua; Swedish: hertig av Finland) was an occasional title granted as a tertiogeniture to the relatives of the King of Sweden between the 13th and 17th centuries. It included a duchy along with feudal customs.

Starting with John III in the 1580s, Swedish monarchs adopted the style of Grand Duke of Finland. This title was used until 1720, revived in 1802–1805, and later adopted by the Russian emperors during the period of the Grand Duchy of Finland (1809–1917).

In the late 15th century, historian Ericus Olai referred to Bishop Kol of Linköping (died about 1196) as Duke of Finland (Colo episcopus Lincopensis et dux Finlandie). The title is anachronistic: in the late 12th century in Sweden, the Latin title "dux" was still used in the meaning of jarl and came to mean duke only a hundred years later (see Swedish duchies). Ericus Olai's claim is not supported by other sources.

Per Olof Sjöstrand has suggested that the title should be understood in relation to the activities in the eastern Baltic for which the Bishop of Linköping was responsible. In 1229, the Pope used him to assist the Bishop of Finland in organizing the diocese, and the first known Duke of Finland, Bengt, was later elected Bishop of Linköping. The Bishop of Linköping had also accompanied the Swedish ledung on their unsuccessful Estonian expedition in 1220. Birger Jarl, who led the second crusade to Finland, was likewise closely associated with the Bishop of Linköping through family ties.

Bengt Birgersson (1254–1291), a clergyman and the youngest son of Birger Jarl, was granted the title of Duke of Finland (dux Finlandiae) around 1284 by his brother, King Magnus Ladulås, whom he had supported in his rebellion against their eldest brother. In practice, Bengt's ducal authority appears to have been largely titular and did not involve a specified territory. Bengt was elected Bishop of Linköping in 1286 and remained occupied with his duties related to that office. Although he retained the revenues associated with the duchy until his death in 1291, there is no evidence that he ever visited Finland or exercised independent rule there.

Valdemar (d. 1318), the youngest son of King Magnus Ladulås (1240–1290), was granted the Duchy of Finland as an appanage at the coronation of his elder brother King Birger in 1302. Birger's instructions to the castellan of Turku from 1303 show that Valdemar held administrative responsibilities in Finland, even if he did not reside there.

Conflict between King Birger and his brothers, dukes Erik and Valdemar, broke out in 1304, and the king took control of all Finnish castles. Valdemar thereafter styled himself Duke of Sweden rather than of Finland, though he continued to use an earlier seal naming him as Duke of Finland. By 1310–1314, the realm had been divided between the king and the dukes. In Finland, Turku and Häme castles were administered jointly by the dukes. In 1315, the dukes divided their territories. Valdemar received the eastern part, which included Turku and Häme castles, Stockholm, part of Uppland, and Öland. He established his ducal court at Borgholm in Öland.

In December 1317, King Birger had his brothers seized at the Nyköping Banquet. Both dukes died the following year while imprisoned. With his second wife, Ingeborg Eriksdotter, Valdemar had a son born in 1316 who died young.