The name of the structure is not an accurate representation of its nature, as it is a palace and not a castle. Another source of confusion arises from the use of different adjectives, with the Polish referring to it as "imperial" (cesarski) and the Germans referring to it as "royal" (königliches). The reason for this distinction lies in the reference to William II, the ruler who built the palace as his provincial residence. While the German name acknowledges him as the King of Prussia, the Polish name recognizes him as the Emperor of Germany. This is because the term "royal" is reserved for the Royal Castle in Poznań, which was the residence of the early medieval Kings of Poland.
Construction of the castle in Poznań, Poland, began in 1905 and was completed five years later in 1910. During the visit of the emperor, the architect presented the keys to the newly built residence to William. The total cost of construction was five million German marks, making the castle the youngest in Europe. During the reign of William, the first and only burgrave was Count Bogdan Hutten-Czapski.
Following the Greater Poland Uprising of 1918-1919 and the restoration of independent Poland, the castle became the property of the Second Polish Republic and was designated as the residence of the Chief of State and later the President of Poland. The building was also used by various organizations, including the University of Poznań, Związek Harcerstwa Polskiego, and the Ministry of Former Prussian Partition.
With the invasion of Poland and annexation by Nazi Germany in 1939, the castle was transformed into Hitler's residence by the German occupiers. The rebuilding was carried out by Albert Speer, and the rooms were changed to reflect the style of the Third Reich. The castle also contained a bunker for 375 people. The rebuilding was stopped in 1943 due to setbacks on the Eastern Front.
During the war, the castle served as a temporary camp for German POWs and later as a barracks for the Polish People's Army. The communist government considered demolishing the castle as a symbol of the German occupation and bourgeois style, but due to lack of funds, only some German symbols were removed and the upper part of the damaged tower was demolished.
After the war, the castle was renamed "New City Hall" and transformed into a center of culture. In 1979, it was declared a historical monument and is protected by law. Today, the castle houses art galleries, a puppet theater, pubs, music clubs, restaurants, and serves as the seat of the honorary consulates of the Philippines, Guatemala, and Slovakia. The castle is also a popular venue for concerts and outdoor movie performances in the summer and is the main venue for the St. Martin's Day parade and celebrations held annually on November 11th. The second floor of the castle remains unrenovated.
The castle was constructed in the Neo-Romanesque style, which was favored by William as the most "Germanic" and symbolizing the grandeur of the Holy Roman Empire. The purpose of building this new residence was to reflect the control over Greater Poland by the Kingdom of Prussia and the German Empire.
The main building, located in the southern part of the complex, was comprised of two wings: the western wing, which was the larger of the two, consisted of apartments and the eastern wing was dedicated to representative rooms. On the ground floor of the western wing, there were rooms for the Court Marshal, Chamberlain, and other members of the imperial court. On the first floor, there were apartments for the Emperor and his wife. A private chapel in Byzantine style, designed by August Oetken, was situated in a tower. The entrance to the chapel was reserved for the Emperor and was located on the western side of the tower. A staircase led directly from the entrance to the first floor. The bedrooms of the Emperor and Empress were connected by a corridor that housed four statues of the following rulers: Margrave Gero, Emperor Otto I, Emperor Frederick Barbarossa, and Duke Władysław II the Exile. The second floor was intended for the Crown Prince (so-called prince rooms). Most of the rooms were connected by a foyer that surrounded an inner courtyard.
The most magnificent room in the representative wing was the Throne Room in Byzantine style. The room was well-lit by huge windows on three sides, positioned between the columns and the arches. Eight statues of Holy Roman Emperors were placed under the arches. The throne, designed in an Oriental style, was located under the central arch. Over the windows was a gallery for guests and the orchestra. The entrance to this part of the castle was from Wałowa Street (now Kościuszki Street).
The north part of the complex, facing Berlin Street (now Fredry Street), comprised of service rooms, a garage, a stable, and a coach house. These structures, along with the two wings of the main building, surrounded a rose garden that included a fountain modeled after the Fountain of the Lions in the Court of the Lions at the Alhambra in Granada, Spain.