The western part of the nave and the church tower are the oldest parts of the asymmetrical Vallstena church. They date from the early 13th century. A new chancel arch was built at the middle of the same century, and around circa 1300 the new choir was built. Reconstruction of the nave also started around this time; the original plan seems to have been to replace the entire nave with a new, larger nave but for some reason the work came to a halt. Similar, half-rebuilt churches are relatively common on Gotland. The sacristy was also built at this time. The interior of the church was decorated with church frescos during the 15th century.
The church and its cemetery is surrounded by a low wall, with three lychgates. The oldest of these dates from the 13th century and display some original sculptured details.
The baptismal font is the oldest fitting of the church, dating from the middle of the 13th century. The altarpiece dates from the 14th century and was acquired when the new choir was inaugurated. From the same century dates a crucifix, as well as a richly decorated chest for donations for the poor. From the 14th century are also to tombstones on either side of the altar, carrying inscriptions in both Latin and Old Gutnish; the latter in runes. A few 14th century wooden statues depicting saints originally from Vallstena Church are today housed in Gotland Museum in Visby.
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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.