The oldest record of Koźle appeared in 1105 and concerned a castellany located in a earth-timber stronghold on the Odra Island. Once again, this stronghold was mentioned in the protective bull of the Wrocław diocese of Pope Hadrian IV from 1155. The town was founded by Prince Kazimierz I of Opole in 1222, while the castle itself in Koźle was probably built some time later, around the third quarter of the 13th century, when a brick residential tower was erected, and then (still in the 13th century) a small circuit of defensive walls. The castle was mentioned for the first time in written sources in 1283, in a document of prince Kazimierz II, which listed members of the princely crew.
In the years 1282-1355 the town and the castle were the capital of the independent Koźle Duchy, which was in the hands of the Opole Piasts dynasty. The Czech king Charles IV of Luxembourg handed over Koźle in 1355 to prince Konrad I of Oleśnica, while in 1473 it was transferred as a fief to prince Henry I the Elder of Podiebrady, becoming a place of the birth of his daughter Margaret. In the late Middle Ages, the castle lost its importance, because in 1477 the King of Hungary, Matthias Corvinus, handed over Koźle to Jan Bielik von Körnitz. The next owner of the castle, under the act of 1490 issued by the Czech king Władysław II Jagiellon, was Putto von Reisenberg. In 1509, his son Wilhelm sold the Koźle principality with the town and the castle to the last prince of Opole, Jan II the Good.
After Jan II’s death in 1532, the Duchy of Opole, along with Koźle and the castle, was inherited by the margrave of Brandenburg, George Hohenzollern. Twenty years later, Emperor Ferdinand I donated them nominally to Queen Isabella of Hungary, and in 1558 he gave them to Otto von Zedlitz of Prochowice. On the order of the latter, the imperial builder Georg von Braun came to the castle, who assessed that the stronghold was uninhabitable, and decided that the cost of erecting a new residence would consume no less than 3,000 thalers. Four years later, Koźle and the castle were pledged by Jan von Oppersrorff, after which he carried out the necessary repair works and erected a new southern wing and a south-west bastion. In the 18th century, the entire town and castle complex was transformed by the Prussians into a great early modern fortress. At that time, the older complex was partially destroyed, with further transformations taking place in the 19th century, and even in 1915, when a tenement house was built on the site of a Gothic residential wing.
The medieval castle in Koźle was situated in the north-west corner of the town, situated on an artificial embankment, raised about 4 meters above the surrounding area. It was separated from the town by a ditch and the area of the outer ward. The town itself was situated near the wide riverbed of the Oder, its numerous arms and wetlands. Despite the favorable hydrographic conditions, at the beginning of the 14th century there was an additional canal around the town, perhaps with the function of a moat. Koźle was also surrounded by a brick town wall, about 1.8 meters thick, with at least a few towers located at irregular intervals. The top of the wall was crowned with battlements and a wall-walk for defenders. Two gates led to Koźle: Odrzańska and Raciborska, both in the form of low towers with hip roofs.
The oldest brick element of the castle was a four-sided, originally free-standing tower house measuring approximately 9.5 × 10 meters. Its corners were reinforced with diagonally located buttresses, but one of them, north-eastern, was later cut off while adding a curtain to the wall. The facade of the building was decorated with a very regular monk bond of bricks, windows 100 to 104 cm wide, two-side spalyed, with only 8 to 9 cm wide openings and pointed finials. These windows were arranged in three walls: two symmetrically from the west, one almost in the axis of the northern wall, and one in the western edge of the southern façade. The location of the last one was dictated by the entrance at ground level in the eastern part of the façade, about 1.3 meters wide, with brick jambs. The western wall was devoid of openings, apart from quite regularly placed putlog holes, visible in the face. The interior of the tower was devoid of brick divisions.
At the end of the 13th century, a small courtyard surrounded by a brick wall was situated on the south-eastern side of the tower house. It was probably erected from the north-east corner, where the buttress was pulled down and a curtain was erected to the east. The circuit was closed quite carelessly, covering the buttress in the south-west corner with a wall almost 2 meters wide.
In the second half of the 14th century, the space around the tower probably became too tight for the prince and his entourage. Therefore, it was enlarged by establishing a plateau with dimensions of about 45 × 46 meters, raised by about 4 meters above the surrounding area . This space was surrounded by a new wall with rounded corners, with a gate on the south-east side, i.e. from the town side. Its brick part was placed on a foundation made of erratic stones, giving the ground floor a thickness of 2.2 meters. In the eastern fragment, the curtain of the castle wall was probably connected with the town wall, through an arcade over the moat, separating the prince’s seat from the town. The wall was topped with a porch topped with a triangular roof (information from the urbarium from 1578) and probably equipped with battlement. Probably as a result of the reconstruction, the older wall and the tower house were demolished.
A Gothic residential wing was probably erected along the northern section of the perimeter. It was a rectangular building, covered with a gable roof covered with tiles, enclosed by two triangular gables of unknown articulation. The remaining buildings at the courtyard of the economic and auxiliary functions had to be wooden.
At the end of the fourteenth century, the entrance to the courtyard was reinforced with a gate tower, founded on a plan similar to a square with external dimensions of 6.5 × 7.8 meters. Its corners from the side of the moat were strengthened by the pair of diagonal buttresses, and the entrance opening of an unknown shape was most likely from the south-east. It was probably closed with a door and a drawbridge, the counterweight of which could be located inside the ground floor of the tower (such a solution is indicated by the carefully shaped joint in the lower parts of the walls and the location of the threshold of the gate opening).
In the second quarter of the 16th century a building was erected along the eastern section of the wall, of a warehouse and economic function. It was built on a plan similar to a rectangle with dimensions of 11.8 × 25.3 meters. Its interior, without divisions, was accessible through three entrance openings from the side of the courtyard. They probably had a rectangular shape and were enclosed in frames of a form unknown today. In the northern part of the building, at the bent of the defensive circuit, a small casemate with two narrow, key loopholes was probably located. The building was covered with a high gable roof set in the north-south axis on two gables. In connection with the construction of the roof trusses, the upper part of the curtain of the medieval wall with the porch of defenders and battlement was probably dismantled.
To this day, mainly fragments of the eastern and southern perimeter walls, the remains of the two wings of the castle and the foundations of the tower, which have recently been rebuilt with a wooden gallery and a hip roof, have survived. Along the eastern wall of the circuit there is a single-storey economic building, erected in the second quarter of the 16th century, and rebuilt in the 17th century, when a three-storey interior layout was introduced. On the south side there are relics of the second wing from the 16th century, while between the buildings there is a courtyard hiding the relics of the former tower house. In addition, in the south-eastern corner of the curtain, relics of the northern jamb of a large opening, probably the castle gate, have been preserved.
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