Duke of Finland (in Finnish Suomen herttua; Swedish hertig av Finland) was an occasional medieval title granted as a tertiogeniture to the relatives of the King of Sweden between the 13th and 16th centuries. It included a duchy along with feudal customs, and often represented a veritably independent principality. Grand Duke of Finland was a nominal royal title used by Swedish monarchs from the 1580s until 1720, which was revived again briefly from 1802 to 1805 (then as Great Prince of Finland) and was also used by Russia's monarchs until 1917. History of actual duchy Bishop-Duke Kol In the late 15th century, historian Ericus Olai claimed that Bishop Kol of Linköping (died about 1196) had been the Duke of Finland (Dux Finlandiae). 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. However, some historians date the small Stenberga Castle in Masku to the late 12th century, when the Novgorodian wars reached Finland and may have resulted in a temporary Swedish military presence in the area. Noteworthy is also that the Bishop of Linköping had some sort of connection to eastern activities during the 13th century. The Pope used him in 1229 to assist the Bishop of Finland in organizing the diocese, and the first known Duke of Finland, Benedict, soon after his nomination was also elected Bishop of Linköping. The Bishop of Linköping had also accompanied the Swedish ledung on their unsuccessful Estonian expedition. Bishop-Duke Benedict Birgerson Benedict (1254–1291), an eccleasiastic, the youngest brother of king Valdemar I of Sweden was granted the Duchy of Finland about 1284 by a subsequent brother on the throne, King Magnus III. Benedict's appointment ended a 35-year-long period of episcopal rule in Finland, effective since the Second Swedish Crusade around 1249. Benedict's local reign did not last long. The Duke, a consecrated priest and the Chancellor of the Realm, was elected Bishop of Linköping in 1286. As far as is known, he bore revenues from Finland until his death but did not attempt any independent rule there. He was the first known holder of the appanage of Finland. Duke Valdemar The youngest son of the late King Magnus III of Sweden (1240–90), Valdemar (1280s-1318), was given his late uncle Benedict's Duchy of