By the early 1300s, Gostynin emerged as an important administrative center of Mazovia. In 1329, it became the seat of a castellan. In 1352, Siemowit III for the first time used the title “Duke of Gostynin”. It was probably during his reign that a defensive castle with a tower was built. Siemowit IV expanded the castle, making it his favorite residence. W³adys³aw II Jagie³³o visited Gostynin twice (1414, 1419). Siemowit IV died here in 1426, and after his death, the complex was rebuilt, with a wooden chapel added to it in 1439.
In 1612, Russian Tsar Vasili IV died at the Gostynin castle, in which he had been kept with two brothers since 1611. In 1793, following the second partition of Poland, Gostynin was captured by Prussian army. The castle, which had for long time been neglected, was pulled down, and its archive was seized by the occupiers. In 1824, the government of Russian-controlled Congress Poland invited to Gostynin 124 German cloth makers, who came with their families. The town began the process of recovery: St. Martin church, town hall and inn were rebuilt, and ruins of the castle were turned into a Protestant church.
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.