One of the most important churches of Mystras is the Cathedral of Agios Demetrios, built in 1280- 1292. It is the oldest church in the city.
This church has a mixed architectural style: on the one hand it has a three-aisled basilica with a narthex and a bell tower, built in the 13th century on the ground floor, and on the other hand, the upper floor is a cross-in-square church, added in the first half of the 15th century. Its interior is decorated with wall paintings in many different styles. This is where the last Byzantine emperor, Constantinos Paleologos, was crowned in 1449.
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.