Before the thirteenth century, the only fortifications in Finland were hillforts.
During that century, Finland became part of the Swedish realm and thus became
part of the kingdom’s larger system of castles. The most important medieval
castles and strongest fortifications in Finland were the Crown castles and the
Bishop’s castle of Kuusisto. At the end of the Middle Ages, there were a half a
dozen large Crown castles, of which those in Turku, Häme, and Vyborg were the
oldest. These fortifications can tell us much about the growth and development of
political power in medieval Finland. In addition, several small strongholds were
founded in Southern Finland, particularly in the fourteenth century. Their history
is poorly known, and in many cases even the name of a minor castle has been
forgotten. Some of these short-lived castles were privately owned. Later, in the
sixteenth century, noble manor houses were built in masonry again but served
hardly any defensive purpose.