San Gianuario is a Roman Catholic church in Marsico Nuovo, Basilicata. It is cited as the co-cathedral of the town along with the church of San Giorgio.
The church is thought to have been erected at the site of a pagan Serapeum, and that some of the capitals of the columns are spolia from such a temple. The site had a pre-Christian cemetery. Documents maintain the Abbey of Santo Stefano was erected here under the patronage of a Count Osmondo during the rule of the Norman Robert Guiscard in the region. The abbey putatively held the relics of San Gianuario, a 4th-century bishop martyred nearby by Diocletian. The abbey however fell into disuse and ruin, leaving behind only this church. The structure has been refurbished over the centuries.
The church houses a number of artworks including a detached fresco derived from the church of San Francesco. The church has paintings by Simonelli, Feliciano Mangieri and Nicola Peccheneda. A stone portal, attributed to Melchiorre da Montalbano, consists of flanking column-pilasters with bas-reliefs of bishops. In a niche above the portal is a half-figure bust of San Stefano. The bronze doors (1699) are by Antonio Masini.
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.