Castillejo de Robledo castle and its lands were property of the Order of Malta until it was suppressed by Pope Clement V in 1311. After that the estate passed to the Knights Hospitaller and then to the residents of the town. In the town there was an old Moorish fortification where the current castle was built in the 12th century. The remains of the original wall are visible and are characterized by a greater thickness than the walls erected later.
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.