According some references there has been a wooden church and stone sacristy in Rauma even since the 14th century. It might be true that stones of the sacristy was used as a part of the Holy Trinity Church. It was built in the 15th and 16th centuries to replace earlier wooden church.
Anyway, church destroyed in a fire in 1640, and the Church of the Holy Cross has served as the parish church ever since. There are still some ruins remaining in the park area.
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.