The castrum in Castiglione delle Stiviere was founded probably in the 9th century, but it is much altered and restored, especially by the Gonzaga family of Mantua in the 16th century. The castle was home to a cadet branch of the House of Gonzaga, headed by the Marquis of Castiglione. Saint Aloysius Gonzaga (1568–1591) was born there as heir to the marquisate, but became a Jesuit. He died tending plague victims in Rome and was buried there, but his head was later translated to the basilica in Castiglione which bears his name.
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.