Gradačac Castle has a fort with walls 18 metres high, built between 1765 and 1821, and a watchtower 22 metres high, built in 1824 by Husein-kapetan Gradaščević on foundations made originally by the Romans. It is finished in the 19th century. In 1831 general rallied the Bosnians against the Turkish occupation and drove the Ottomans out to Kosovo, winning Bosnia its sovereignty for the coming year. Therefore, fortification has great historic importance for Bosnians. It has been recently renovated.
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.