Christiansø church was first consecrated in 1685 when the island's fortifications were completed. Serving the garrison, it was initially located in a small floor room in the fortification tower where it was used until 1821. It was then moved some two hundred metres to the east to its present location on an irregular quadrangular plot surrounded by fieldstone walls.
The small rectangular granite building was rebuilt and enlarged in 1852, a porch being added on the western side. Comprehensive restoration work was undertaken in 1928 under architect Christian Olrik. The main entrance was widened and a gallery was added inside. The four straight-sided windows on either side of the nave were slightly reduced in size and given a rounded finish. The ceiling consists of a plastered, wooden barrel vault.
In the south-west corner of the churchyard there is a free-standing bell tower with two bells. Typical of the Bornholm style, it consists of a fieldstone base and a half-timbered belfry.
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.