The Oratory of San Marco is a Byzantine-style oratory situated in the old town centre of Rossano, a frazione of Corigliano-Rossano.
The church was built in the 10th century by St. Nilus the Younger as a place of retirement for nearby eremite monks and is one of the most important testimonies to Byzantine art in Italy. It is the most ancient monument in the city and was originally dedicated to St. Anastasia. It has a Greek cross plan with five characteristic domes on cylindrical drums and, in the past, the entire building was supported by very thin columns then these were covered with cement after restoration works. Between 1928 and 1934, during the restoration works, a fragment of a fresco picturing a Virgin Hodegetria was discovered.
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.