A defensive brick building in Jarocin, defined in a 1496 document as a fortalitium, had presumably already been erected by the beginning of the 15th century. This building was then rebuilt, extended and eventually demolished. The building known locally as skarbczyk (the jewel box) is all that remains of it today. A lot of decorative fragments of Gothic furnace tiles, attesting a once opulent castle interior, have been uncovered here during the course of excavation work.
There is a two-storey brick and plaster building laid out on a rectangular plan and surrounded by what used to be moats by the pond in the southern part of the park. The domed turret adjoining the body of the building from the west was added a good while later. The main body has a tiled pitched roof. The walls are supported by strong corner abutments and framed rectangular window openings. A stone bas-relief of the Leszczyc coat of arms of the Radoliński family hangs above the portal on the tower elevation. The vaulted rooms inside have been preserved.
It is now the Jarocin branch of the Regional Museum.
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.