Hämeenlinna Church was built in 1798 as a rotunda modelled on the Pantheon in Rome. It is designed by Frenchman L. J. Desprez, the court architect of Sweden. The altar stood in the middle of the amphitheatre-shaped church, and the pulpit was above the sacristy door. Hämeenlinna church is one of the best samples of so-called Gustavian classism style in Finland.
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.