Castellaneta Cathedral is dedicated to the Assumption of the Virgin Mary. It is the episcopal seat of the Diocese of Castellaneta. The first cathedral on the site was initially dedicated to Saint Nicholas of Bari, and dated at the latest from the Norman occupation of the last decades of the 11th century. In the 14th century, it was replaced with a Romanesque structure with a basilica layout of a central nave and two aisles separated by columns, all three terminating in semicircular apses. The dedication was changed at this time to the Assumption of the Virgin Mary.
Three chapels were later added: the Chapel of the Most Holy Sacrament (Santissimo Sacramento) in 1538 and the Chapel of Mary the Consoler (Santa Maria Consolatrice) in 1643, both founded by confraternities; and the Chapel of the Most Holy Crucifix (Santissimo Crocifisso). There is also a chapel dedicated to Saint Nicholas, with Romanesque capitals. In 1771, a new white limestone façade was added. Today, the bell-tower retains some of the Romanesque-Gothic elements. In the 18th century, new polychrome altars were built. The Bishop's Palace is adjacent.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.