Buildings at the site of Somma Lombardo Castle date from the 9th century and the fortress from the 13th century. In 1448, the brothers Francesco and Guido Visconti, took refuge in this town and castle from the forces of the Ambrosian Republic. They divided the landholdings and portions of the castle. The fortress has been amalgamated from adjacent residences, all once surrounded by a single moat. From the brother Francesco, who owned the newer portion of the castle, descend the Visconti di San Vito; while from Guido, who owned the lower and older portions of the castle, descend the Visconti di Modrone.
The San Vito castle contains frescoes attributed to the school of Camillo Procaccini and an altarpiece by Cerano. The castle also has an extensive collection of barber plates.
Parts of the castle are used for private events and open for guided tours.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.