The beginnings of the fortified stronghold on the territory of present-day Grudziadz go back to the 10th century. It was first mentioned in historical sources in 1065. In 1207 the stronghold was ruled by Konrad of Masovia who, in 1218, bestowed Chelmno Land and the stronghold to Bishop Christian. In 1231 the town was conquered by the Teutonic Knights. In 1299 construction of the castle was completed and a town was erected around it.
The town was partially ruined several times during attacks by Pomeranian Dukes (1242, 1244), the Prussians and the Lithuanians (1278-1281). The seat of the commander of the Teutonic Knights was established in Grudziadz. In the 14th century the town was surrounded by a thick, double wall with 10 towers and 4 fortified gates. Moats were dug along parts of the wall. The town became a center of grain trade because of its favorable location on the Vistula waterway. The large granaries on the Vistula River were first mentioned in historical documents in 1365.
During the Polish-Swedish War (1655-1660) the Grudziadz castle became Charles Gustav’s headquarters. In 1711 Peter I, tsar of Russia lived there. From the 16th until the 18th century the town’s development was hindered by wars, plagues, floods, fires, as well as by competition from other developing towns nearby, in particular Torun. In 1772 Grudziadz passed under Prussian rule and soon after became a garrison town, in large part thanks to the mighty fortress built between 1776-1788. King Fredrick William III found shelter in Grudziadz after having lost the Battle of Jena against Napoleon. The town began to deteriorate with the decline of trade on the Vistula. Further destruction occurred between 1806-1807 when the town was under siege by the French for 5 months.
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.