Canosa 'castle' is actually the acropolis of ancient Castrum Canus. The three great towers are the ruins of the eponymous estate located atop the hill overlooking the valley Ofantina. Originally a place of worship and pre-Roman fort, built of tufa blocks was rebuilt as a bastion of the same materials by the Grimaldi. Last owners, from 1856, were the Prince of Canosa Capece Minutolo of Naples, and remained until 1948. The wear of the blocks that compose it and the color denotes the passage of these various civilizations that have developed the structure in different epochs. The castle has also reported damage after the devastating bombing of the Second World War. Along the steep hill of the Acropolis, there is the old part of the country, with its narrow streets and staircases. At the southern base lie the remains of a Roman amphitheater.
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.