The structure of the arsenal consists of two large stone-built halls with vaulting supported by repeated pointed arches. The vaulting rests on ten piers, originally there were twenty two, the missing twelve and the structure they supported having been lost to centuries of coastal erosion. The main function of the arsenal was the building, repair and storage of warships. Amalfitan war-galleys were among the largest to be found in the Mediterranean during the Early Middle Ages.
The building now contains architectural and sculptural remains, a row-barge used in the Historical Regatta, a number of models of ships and it also acts as a venue for visual art exhibitions. Starting from December 2010, the Ancient Arsenals of Amalfi host the Compass Museum on the premises of the two aisles of the building, which were spared by the Amalfi seaquake of 1343.
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.