Marostica area became under the rule of Cangrande I della Scala in 1311. Next year he founded two castles in Marostica, the lower (Castello Inferiore) and upper (Castello Superiore) castle.
The lower castle in the city center is rectangular. After the War of the League of Cambrai, the mayor moved his headquarters from upper to lower castle. The upper castle is a square form building with four little towers on the sides and a large central tower.
There is a 1800m long wall connectiong these two castles.
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.