The Espoo Cathedral is a medieval stone church built in the last half of 15th century. The church is thus the oldest preserved building in the city. The church was originally designed in by an unknown "Espoo master" and built between 1485 and 1490 under his supervision.
The only remaining parts of the medieval church are the eastern and western parts of the nave. The weapons room was removed between 1804 and 1806 and certain other parts of the church, including the original sacristy, were taken apart between 1821 and 1823 when the building was converted into a more spacious cruciform church.
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.