Stenberga was an ancient castle built probably in the 14th century. It was fist mentioned in 1389 and built probably by Jakob Abrahamsson, the bailiff of Turku. In 1438 the castle was donated as the site for Naantali Bridgettines Abbey, but in 1443 the abbey was decided to move to the Ailos. The castle was located to the rock hill near Masku River. There has probably been a 13 x 13m tower made of stone.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.