Åbo, near the coast in the south-west is the oldest town in Finland. The River Aura flows through the town. Åbo was founded in 1229. As early as in 1276, the town was the Episcopal seat of Finland. Earlier, Finland had belonged to the archdiocese of Uppsala.
Around 1280, Åbo Castle was built on the mouth of the River Aura. First, it was a high ring-wall which had a tower with a gate. At the same time, the cathedral of Åbo was built. It was consecrated in the year 1300. During the Middle Ages, there was a Dominican friary, a hospice, a hospital for lepers, and, next to the church, a school. This school was the first school in Finland.
During the Middle Ages, the Hanseatic League had interests in Åbo. The town was an important port for reloading cargo coming from Tallinn and Viborg. Mainly fur, forest produce and flax was exported from this Finnish port.
Between 1556 and 1563, Gustav Vasa ´s son Count Johan stayed for long periods at Åbo Castle.
Åbo was the chief town in the eastern part of the Swedish kingdom. In 1623 the Åbo Court of Appeal was founded, and, in 1640, the university, Åbo Academy.
After the Swedish-Russian war in 1741-1743, peace was made in Åbo. Sweden lost the war and had to accept the claims made by the Russians.