Frankenberg Castle was constructed during the 13th century and historically it was the seat of a Vogt, local administrator. Until the end of the 19th century, the castle consisted of a broad forecastle, a farmyard, and a main castle (which was completely surrounded by water).
With the introduction of the French Constitution of 1793, Frankenberg Castle lost its status as a fief of Jülich. Between 1834 and 1838, the property underwent comprehensive renovation and modernization.References:
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.