The castle was ruled in different stages of its history by the castle sheriff, commander, regent, duke or governor-general. Its significance as a defensive fortress and administrative centre varied throughout the ages according to the political situation. Only once did the castle actually figure in the defence of the realm. This was when Russian invaders from Novgorod destroyed Turku in 1318. On the other hand, it frequently played a role in internal struggles for power within Sweden and the Kalmar Union. Not until the end of 16th century did it really enjoy peace. The castle lost its status as an administrative centre in the 17th century after Per Brahe's period as governor-general of Finland came to an end.