Château de Teillan was built probably in the 9th and 10th centuries to the site of an ancient Roman castrum called Villa Telianum. In the 12th century it was sold to the abbey of Psalmody. The chateau is surrounded with a landscape park from the 19th century where are located Roman steles, milestones and a waterwheel. Today Château de Teillan is privately owned, but open in the summer season.
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.