Construction of the St. Nicholas Church began about 1165. It is named after St. Nicholas, patron of travelers and merchants. It was built originally in the Romanesque style (with twin towers) but was extended and enlarged in the early 16th century in the Gothic style. The Baroque main tower was added in 1730; the portal dates from 1759.
From 1784 to 1797 the interior was remodeled by German architect Johann Carl Friedrich Dauthe in the Neoclassical style. The church has been a Protestant seat since 1539 after the Protestant Reformation, but today the Catholic Church is also allowed to use it.
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.