The Uniejów Castle was built in the years 1360-1365 replacing an old wooden fortification that was destroyed during the wars with the Order of Teutonic Knights in 1331. The fortified castle was erected on the initiative of Abp. Jarosław Bogoryja Skotnicki. A few fundamental periods can be identified in the time of its construction.
The Uniejów Castle was based on a rectangular plan with dimensions of 29 m x 24 m. Its brick walls were erected in the Gothic arrangement on a foundation formed from field stones. However, the funding program established by Jarosław from Skotniki was quite modest. The western curtain of the unit was occupied by a residential building that was 10.5 m wide. The building had at least three floors: basement, ground floor and first floor which served as a residential area and had two chambers. An interesting element was a buttressed break with semi hexagonal termination from the side of the courtyard. The ground floor had an entrance hallway, while the first floor was probably home to a chapel. We do not have any information concerning the exterior and interior design of the residential building.
The main defensive component of the castle was an over 25m high tower, protruding in front of the face of eastern curtain walls that were slightly bent towards the east. The tower supported by buttresses had a diameter of 9 meters. Its entrance was located around 12.5 m above the courtyard. Wooden stairs led to a defensive gallery surrounding the castle courtyard from three sides. The interior functional floors of the tower were connected by a stair enclosure in the north-west counterfort. It was a communicating passage between floors - from the lower - prison floor to the higher - guard’s platform. The surrounding wall was 13m high and the crucial place, which was the internal gate, was guarded by a tower.
It is assumed that the next stage of transformations of the castle complex took place in the 15th century. It consisted in extension of the functional program with improvement of defensive values of the building. The extension of the western residential wing comprised two three-story towers and the third one in the northern-eastern junction of the structure. The castle was reinforced with an additional external low wall that combined new towers. Thanks to that, the defensive system of the castle was largely strengthened. After the renovation, the area occupied by the castle increased by around 660 m2. In the 15th or 16th century at the latest a small masonry gatehouse which served as additional defense element was built.
The corner towers-annexes played a defensive role, but probably also a residential function. Behind the western wing they were connected by passages in the walls.
The direct cause of subsequent transformations was the necessity to eliminate destructions caused by the fire in 1525.
The Uniejów Castle served a wide variety of functions. Its vaults served as a prison for the Hussites who in 1422 were captured by order of Pope Martin V. It is also said that in 1485, by order of Abp. Jarosław Bogoria from Skotniki, a famous builder and sculptor from Gdansk, Hans Brand, was kept prisoner for more than one year. The castle retained its original form till the mid-15th century, when it was expanded and its fortification was adjusted to the use of firearms. Therefore, when in 1454 the Thirteen Years’ war broke out, Uniejów became a place where the treasures of the Gniezno Church was stored. The entire treasure was fitted in a few wings. One of the chests contained the head of Saint Adalbert of Prague, the head of Gereon, relics of St. Ursula’s companions and martyrs, St. Adalbert of Prague’s hand, St. Stanislav’s hand and its ring, a large gilded monstrance and a few chalices, including the gold chalice of Abp. Jarosław Bogoria from Skotniki. When in 1456 the regular army began to pose a threat to archbishopric’s estate, the Gniezno Chapter again decided to bring its treasures from Gniezno to the Uniejów Castle. They were stored here a few times more: in 1479, 1493, 1502, 1509, 1511, 1513, 1517, 1519. Given the refugee function of Uniejów, on 22.10.1520 the Chapter decided that the Castle would be strengthened and filled with mercenaries.
It is difficult to say whether the intentions were ever fulfilled, however, the fact is that the castle burnt down in 1525. In this period the castle started to gradually lose its significance. The archbishops more often resided in Łowicz. Uniejów became the seat of starostes. In fact, one of them - Stanislav from Gomolin executed another castle extension. The works lasted a few years and were finished in 1534. A memento of Stanislav from Gomolin and his work is a commemorative plaque with the Jelita coat of arms set in one of the Gothic arch recesses in the courtyard. In this time, new polychrome decoration of the castle’s chapel was probably made, whose fragments that survived to this day present, among others, martyrdom scenes of St. Adalbert of Prague.
According to a description by canon J. Kokalewski, which dates back to the year 1556, the castle built on a four-sided plan, had quite high external and internal walls, firmly supported by thick pillars. It had a strong support system. There were also baths, buildings, small chambers and other rooms, such as an iron storehouse. It had double merlons - external and internal - intricately and well constructed with a high tower with wooden rungs leading all the way up to the top. The merlons were covered by a decorative roof tiles laid at the cost of the archbishop, just like the roofs of the castle building. The castle was equipped with 3 cannons, 14 new and 5 old harquebuses, as well as 10 matchlocks and a powder keg.
In the bailey below the castle there was a large house erected by Abp. J. Latalski with a big steam bath on the first floor, opposite which there was another smaller one for the court servants and farmhands. There was a second house in the bailey, which apart from other rooms, featured also another bath. It apparently also had a kitchen and a stable as well as other buildings, among others, a bakery and a brewery.
The Uniejów Castle was a seat of administrative authorities who governed the town and church barns for the owner. It was a staroste and his deputy - called a burgrave.
Eventually, most of the castle’s fortification features were lost in the first half of the 17th century. The initiators of works performed in 1639 and 1645 were two primates: Jan Wężyk and Maciej Łubieński. The so-far autonomous residential buildings surrounding the courtyard were architecturally merged. This was achieved by development of the land between the south-west walls that was unoccupied before. The facade arrangement was unified by covering them with plaster and making new, large window holes fitted with jambs. The gateway gained a new baroque design. It was decorated with two coats of arms - Pomian and Wąż. Adam Miłobędzki dates the castle alteration to the years 1638-1642 and classifies it as a provincial Baroque trend.
The three-winged arrangement obtained additional height by raising or lowering individual elements. The entire structure was crowned by a ceramic roof. The main tower also underwent alterations. At the times of M. Łubieński they were covered by a baroque dome.
The good times for the Uniejów residence was discontinued in the middle of the 17th century. Events that affected the turn of events were related to the Swedish invasion in 1656 and Lubomirski’s Rebellion. At the beginning of the 18th century further destruction and devastation ensued. In particular the fire in 1736 inflicted immense losses on the building. The main reason for the renovation executed by Archbishop Krzysztof A Szemhek in 1745 was to secure the run-down building of the castle. The works probably did not introduce significant changes in the form of the building.
After secularization of primate’s estate by Prussian authorities, the castle was used in a limited scope. This changed in 1836, when the Tsar’s government granted Uniejów estate to Gen. Karol Toll. The beneficiary himself never visited his estate, however his son Aleksander did. In 1848 the new owner conducted renovation by erecting, among others, new roofs. We do not know the scope of works undertaken in the interiors. They must have concerned the intention of transforming the castle into a summer residence of the Tolls. In 1848 a natural landscape park was established. As a result of works executed in the second half of the 19th century, it occupies the area of around 37 hectares.
The Tolls remained the owners till 1918. Due to unknown circumstances, the residence was devastated in this period. During the interwar period the castle buildings served a function of a guesthouse. After the last war the castle was used as a warehouse for fertilizers and crop. Only in 1957-1967 restoration and adaptation works were executed based on the design by H. and I. Ziętkiewicz.