Saint Alexander’s church in Rinsumageast was built of tuffstone originally in the 11th century. The semicircular choir was built in the 12th century followed by the nave and the tower dates from the 13th century. Under the choir is a crypt, uniek for the north of the Nederlands. The church was enlarged in ca. 1525 with the replacement of the southern aisle by a new one. The monumental Pipe organ was built in 1892 by Bakker & Timmenga.
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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.