Kalmar Church was built of granite in the late 12th century. Around 1300 it was enlarged and modified to the aisleless Gothic church. In 1485 famous Albertus Pictor decorated walls and vaults with murals. Frescoes were restored in 1958 and still visible. Th current tower was added in 1830. There is font with a cuppa, made of red sandstone, from the late 1100s and medieval wooden sculptures (like a triptych from the mid-1400s) in the church.
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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.