The castle was built around the middle of the 14th century on the initiative of the archbishop of Gniezno, Jarosław Bogoria Skotnicki. The hierarch took up the archbishop’s stool in 1342 and from that time became famous among numerous foundations, as a perfect organizer and builder of churches and episcopal residences (among others, he was the initiator of the reconstruction of the Gniezno cathedral). By building defensive structures such as Uniejów, Jarosław also completed the construction action of king Casimir the Great. Apart from the military function, the castle also had an administrative role. In 1376, there was a famous synod with the participation of a many clergy in which a special emissary of Pope Gregory IX took part, nuncio Nicholas, bishop of Majorca. Its goal was to tax the clergy for a crusade against the Turks. The castle was also a shelter for the treasury and the cathedral archives, which were transported to Uniejów in times of threats and wars. The fact that the castle was conquered and plundered in 1381 by Bernard of Grabowo proved that even then treasures were not completely safe.
In the middle of the 15th century it was greatly expanded and re-acquired by Wawrzyniec Kośmider Gruszczyński during the war of the Gruszczyński family with bishop Zbigniew Oleśnicki about Koźmin. In 1525 the building destroyed the fire. The restoration combined with the conversion of the castle took place in 1534 on the initiative of the starost Stanislaw from Gomolin. Further work was carried out by archbishops in the 17th century, which eventually changed the fortress into a renaissance-baroque mansion. After the secularization of church property at the end of the 18th century, a large part of the castle was abandoned and only in 1836 the tsarist government handed it to General Aleksander Toll. During the interwar period, in the monument was functioning a guesthouse. In the years 1956-1967 the castle was rebuilt after the war losses.
The castle was situated on the left bank of the Warta River on a small hill. On the one side, it was secured by a river bed, which approached almost to the castle itself, and from other sides by wet and marshy areas. The moat was dug out as an outer zone of defense. The only communication connection with the town was provided by a nearby bridge. In the fourteenth century, the castle consisted of a quadrilateral perimeter of the walls 23 x 29 meters, built of bricks on the foundation, of which stones were joined with lime mortar. From the south there was a gate, and on the western side of the cobblestone courtyard a two-room, three-storey residential house (10.5 x 23 meters) to which the chapel was added. It was connected at the level of the floor with a defense porch in the crown of the walls, the top of which probably took the form of a battlement.
The main tower with a diameter of 9 meters was erected outside the wall in the middle of the eastern curtain. Due to the high altitude (35 meters), it was reinforced with three buttresses, and originally the only entrance to it was located at a height of 13 meters above the level of the courtyard and was accessible by a footbridge from the crown of the defensive wall. Vertical communication was provided by a spiral staircase placed in the north-west buttress, but it was not directly connected with the entrance, because it started at a height of 4 meters above the floor and led to a defensive level at a height of 25 meters.
Around the middle of the 15th century, two quadrilateral, three-story residential towers were added to the main residential house in the corners. They were connected with each other by an outer wall, closing the west zwinger. The rebuilding also included the southern part of the castle. A four-sided gate tower, connected by an external wall with a main tower, was built on the site of the former gate. The new fortifications separated about 6.5 meters width zwinger.
In the first half of the sixteenth century, the south-eastern part of the zwinger was built up with a new residential building, which, having the shape of the letter L, reached the main tower, which was then raised by the next defensive level. On the north side, the new economic wing was adjacent to the tower, closing the whole castle in the shape of a regular quadrilateral. Communication between individual wings was provided by the inner courtyard. The south wall had two entrance portals: one to the gate tower and the other leading to the south zwinger. On the opposite side of the courtyard, on the axis of the main entrance there was a narrow passage to the northern zwinger. Three ogival blendes were visible above it. From the northern zwinger led the entrance to the cellars of the north-western tower and symmetrically to the opposite economic building. In addition, the upper storey of the main house was connected with the south-east wing through the porch on the wall and the gate tower.
Despite the fact that castle has survived to modern times in a highly transformed form, it still has readable medieval elements, among others gothic main tower and cramped, inner ward. It now houses a conference center and a restaurant. It is open to the public, but to a limited extent.
Leksykon zamków w Polsce, L.Kajzer, S.Kołodziejski, J.Salm, Warszawa 2003.
Krantz L., Zamek w Uniejowie, Poznań 1980.