Eynhallow Church is probably the ruin of a 12th-century Benedicitne monastery. Because of the name of the isle it is likely that Eynhallow was an important religious centre. Eyin-Helha is Old Norse for Holy Isle.
Eynhallow Church was deserted before the reformation (circa 1560). The church was converted into dwellings in the 16th century. In 1851 the inhabitants of Eynhallow were transferred elsewhere and the church and other buildings were stripped of their roofs. The ruin was consolidated by W.R. Lethaby in 1897.
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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.