The castle was erected on the site of a hillfort in the northern part of the Odra island. The construction began on the initiative of prince Kazimierz I in 1228. The works were continued by his son Władysław I and grandson Bolesław I, who in 1273-1289 built the main castle house. Around 1300, a cylindrical Piast Tower was built. The castle was the seat of the Opole Piasts until the death of its last representative, Jan II the Good in 1532. In 1557-1566, eastern and southern wings were rebuilt at the initiative of Jan Oppersdorf. At the end of the 16th century, the castle was enriched with fortifications that made it a fortress during the Thirty Years War. Unfortunately, in 1615 the castle was destroyed by a fire. The dilapidated residence began to be dismantled. First, in 1730, the western wing was removed, and in 1838-1855 the castle walls were pulled down and the moat was filled up. In 1928-1931, by the decision of the German authorities, the rest of the castle was pulled down, keeping only a cylindrical tower, thanks to the protests of the Polish minority.
The castle was one of the first brick fortified strongholds in Poland. It consisted of a polygonal outline of brick defensive walls, repeating the course of the wooden-earth ramparts of the hillfort, a four-sided tower located on the perimeter of the walls, located on the north, a four-sided, free-standing building measuring 12×15 meters in the south-west corner of the foundation and added to it from the north, the main castle house. Around 1300 at the entrance gate, in the south-east part of the foundation was built a cylindrical tower, today called the Piast Tower. It is set on a deep, 6-meter, stone foundation. Originally, the entrance was a few meters above the courtyard level and was accessible from a wooden gallery. Inside, there was a prison dungeon in the lower storey, and a guardhouse above. In the 14th-15th centuries, more buildings were added next to the perimeter walls in the southern and western part of the courtyard, also expanding the gate area.
Today, the only remnant of the castle of the Opole princes on Ostrówek is the cylindrical tower known as Piasts Tower, which is the city’s symbol. Currently, it is squeezed between the former registry building and the amphitheater. Despite the fact that here and there you can read that the pre-war office building is one of the most magnificent examples of modernist architecture, it actually disfigures the castle surroundings and has nothing to do with the historical appearance of the island. The tower itself, after a recent refurbishment, has been made available for sightseeing, which is presented in an interesting way, despite the lack of significant exhibits. Unfortunately, during the restaurant, the ahistorical crown of the tower was not changed.
Leksykon zamków w Polsce, L.Kajzer, S.Kołodziejski, J.Salm, Warszawa 2003.