The first documentary reference to Santa María de Piasca is a donation from 930 making reference to a basilica just founded on the site. Little over a decade later, in 941, an agreement was recorded between 36 nuns and an unknown number of monks under an abbess Aylo, telling us that the monastery housed a community of both sexes. The monastery's dual character faced several oscillations, with the nuns leaving and returning twice. The archeological evidence of the original monastic buildings shows a small single nave church and separate spaces for the two groups.
A foundation stone records that the current church on the site, the Romanesque edifice, was dedicated in 1172 under a prior Petrus Albus. By this point the monastery had been incorporated into the larger Cluniac monastery of San Facundo y Primitivo de Sahagún (in 1122) and brought under the Benedictine Rule. The inscription also names the master of the project as Covaterio. The church has two sculpted portals, the west and the south. The portals have most likely been somewhat reconstructed, possibly with elements exchanged between the two. The triple arcade on the west façade has obviously been renovated as the central sculpture of Mary is from the sixteenth century. The two apostles (Peter and Paul) to her sides may have originally flanked an image of Christ, forming, as Ruth Bartal suggests, an abbreviated apostolado.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.