Excavations have not been carried out on the site since the early 20th century, which has given room to dispute the castle's age. Some historians see it as a 14th-century construction, while others date it to the late 12th century, when King Canute built similar-looking small defensive castles in various parts of Sweden. According to more or less vague chronicles, Finland seems to have been under special military attention by Danish, Swedish and Russian forces in the 1190s, thus giving the possible context for the construction of the castle. Historian Ericus Olai claimed in the late 15th century that bishop Kol of Linköping (d. 1196?) had been the Duke of Finland (Dux Finlandiae), which however can not be confirmed from other sources. Also noteworthy is the castle's strategic position clos