Aosta Cathedral was originally built in the 4th century. In the 11th century the Palaeo-Christian structure was replaced by a new one, dedicated to the Assumption of the Virgin Mary and Saint John the Baptist. The architecture of the cathedral was modified during the 15th and 16th century.
The present façade, in Neoclassical style, was built between 1846 and 1848. The structures remaining from the Romanesque period are two clock-towers and the crypt, and also the remaining part of an Ottonian fresco cycle on the church ceiling.
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.