Castelseprio or Castel Seprio was the site of a Roman fort in antiquity, and a significant Lombard town in the early Middle Ages, before being destroyed and abandoned in 1287. It is today preserved as an archaeological park.
Castelseprio originated as a Roman fort that commanded an important crossroad. During the early Middle Ages, the Lombards occupied the Roman fort, turning it into a fortified citadel or small town. At one point coins were minted there - a sign of its importance. The Church of Santa Maria foris portas ('foris portas' meaning 'outside the gates' in Latin) which contains the famous frescoes, lay just outside the walls of the citadel. The early dedication of the church to Mary is an assumption; the first documented mention of a church dedicated to Mary in Castelseprio comes from the 13th century.
The whole citadel was completely destroyed by Ottone Visconti, Archbishop of Milan, after he captured it in 1287, to prevent it being used again by his rivals. Investigations into the church, which began in 1934, finally uncovered the famous Byzantinesque frescoes below later plaster in 1944.
The whole area is now an archaeological zone containing the remains of the walls and of the much larger three-aisled 5th-century Basilica of San Giovanni Evangelista. There is also a baptistry of the 5th to 7th centuries dedicated to St. John the Baptist. This has two fonts, perhaps for the use of different Rites, and is octagonal with a small apse to the east. A third Church of San Paolo has a central hexagonal plan and was built between the 6th and 12th centuries. There are some ruins left from the castle. Nearby is a large tower, once used as a convent.
The fame of Castelseprio lies in the Early Medieval frescoes contained in the small Church of Santa Maria foris portas. These frescoes are of exceptional rarity and artistic significance. Hidden for centuries, the frescoes were only rediscovered in 1944. In 2011, the church - and the castrum with the Torba Tower - became a UNESCO World Heritage Site as part of a group of seven inscribed as Longobards in Italy, Places of Power (568-774 A.D.)
When the Church of Santa Maria foris portas was investigated in 1944, it was found to contain, as well as later frescoes, a highly important and sophisticated cycle of fresco paintings showing very strong Byzantine influence. The dating of the frescoes and the origin of their painter or painters remain controversial, although the first half of the 9th century seems to be emerging as the most likely date.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.