The castle was probably erected in the second half of the 14th century on the initiative of king Casimir the Great, perhaps after 1362, when a nearby town was founded. It stood on the site of an earlier tower, which was surrounded by wooden fortifications, probably erected during the reign of Władysław I the Elbow-high in the early fourteenth century or a little earlier by Wenceslaus II of Bohemia, who ruled Wielkopolska region since the coronation in 1300. In the latter case, the discovered traces of a fire could be associated with Władysław’s recapture action.
The castle in Koło secured the road leading from Wielkopolska towards Łęczyca through the Warta valley. It was the seat of starosts, of whom the first known was Krystyn from Koziegłowy, also known as Krzon. The castle experienced its heyday in the 15th century, when it was visited by kings and the nobility of Wielkopolska gathered in it at the congresses. On the basis of the archeological findings, it can be stated that intensive construction works were carried out then at the residential tower and inside the perimeter of the walls. In 1476 king Kazimierz Jagiellończyk rewarded princess Anna Sochaczewska, giving her for a life time of Brdów, Boleniów and Koło along with the castle in exchange for the lost Sochaczew Duchy. After six years, Koło returned to the starosts, who resided there until 1577.
At the end of the 16th century, the castle lost its importance, and in 1655 it was destroyed during the Swedish invasion. In the eighteenth century, it became the property of the Bernardines, who began to dismantle it, leading along with the destructive action of the river, to the state of ruin.
The castle was erected on a small hill on the left, marshy bank of the Warta River, about 3 kilometers from the town. It was a rectangular (with a slightly bend northern curtain) structure measuring 30×50 meters with the main tower in the south corner, slightly extended from the face of the defensive walls. It is square in the base, higher cylindrical. Today, it has a height of 16-17 meters and dimensions in the plan of 8.2 x 8 meters. The original entrance to it was located at a height of 2 meters above the level of the defensive porch on the crown of the south-western curtain. A staircase in the wall thickness led to the upper terrace. Traces of the beams’ nests indicate that timber, flat ceilings divided the tower into two floors. It is not sure how it was topped. If you believed the iconography, it had machicolation and battlements and a conical ceramic roof. In the northern part of the outer façade, a timber latrine probably functioned.
Next to the corner tower (at a distance of about 8 meters) in the eastern curtain there was a four-sided gatehouse building with a side length of 9 meters and a wall thickness of 1.8 meters. It was supported by two diagonal buttresses and advenced in front of the perimeter. The entrance led through a gateway, 1.8 meters wide, probably preceded by a drawbridge. In addition, there was a small wicket gate in the south-eastern wall.
The courtyard of the castle was built with wooden or half-timbered buildings and was not paved. It was surrounded by walls, wchich present height in the highest place reaches 10 meters. They were set on a stone pedestal, passing over 1.8 meters into a brick wall, between 1.9 and 2 meters thick. In the upper part it narrowed, eventually passing in the breastwork topped with battlements (they were 2.15 meters high). After the surviving sockets on the beams in the base of the breastwork, one can guess that the porch of the defenders has been widened with a timber part. It is not known whether the porch in the crown of the walls was roofed.
At the western curtain of the castle, foundations of the older tower house on the rectangular plan were found, built of sandstone ashlar and bricks on a foundation of erratic stones. Before the castle was created, it was an free-standing housing and defense facility. It had dimensions of 11.8 x 13.2 and a wall thickness of 2.5 meters. It had a basement and had a division into two rooms on ground floor: a larger one with dimensions of 7.2 x 6.8 meters and a smaller 8.8 x 2.2 meters in which the elements of well were discovered. In the middle there was a passage with a width of 1.3 meters. The height and division of the upper storeys is not known, it can only be assumed that tower house had two or three floors. The entrance to it was placed from the south-eastern side.
The entire castle was originally surrounded by an irrigated moat. On the outer bailey, relics of wooden fortifications protecting the castle from the floodplain were found.
The ruins of the castle are located on a small hill in the Warta river valley and consist of a southern wall line, a fragment of the north-western curtain with foundations of a residential and defense tower house, relics of the south-eastern curtain and a corner tower which current height is 17 meters. Entrance to the ruins is free.
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