Santa Marta was initially built in the late 15th-century but rebuilt at the end of the 16th century by the Confraternity of Santa Marta, a confraternity of disciplinanti (or flagellants). To the right of the entrance, they built an oratory.
Of the original decoration only one altar remains, and traces of frescoes in the presbytery and some lunettes in the walls of the oratory. Deconsecrated after World War Two, it became the property of the Commune of Ivrea in the 1970s, who converted it into a conference hall. The Baroque portal was moved to the parish church of San Bernardino in Ivrea.
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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.