Either Lütold V von Regensberg or his son Ulrich established the fortified town of (Neu)-Regensberg around 1250. Ulrich died around 1280, and his son Lütold VIII had to sell Regensberg to Habsburg-Austria in 1302. The Habsburgs mortgaged the castle and town several times, and in 1407 the so-called Herrschaft Regensberg was acquired by the city of Zürich. From 1417 the castle became the seat of the bailiff of the bailiwick of Regensberg. On 6 June 1443 the council of Zürich forced their troops and the citizens to defend the fortified town, three days later the castle was conquered during the Old Zürich War by Zürich's contrahents, but not destroyed, and some months later manned again by Zürich troops.
On 9 September 1540 the town, but not the castle, was destroyed by fire, because it was separated from the Oberstadt by a ditch. The upper castle was rebuilt in the following year. From 1689 the castle and the upper town were fortified according to then modern standards. On 13 March 1798 the French revolutionary troops forced the council of the city republic of Zürich to abdicate, and the country bailiwicks were dissolved. After the end of the short-lived Helvetic Republic, Regensberg became the district capital, and the castle was the seat of the cantonal authorities, and in the main building there was the county jail until 1863.
Regensberg was designed as a fortified castle town and built by then modern contemporary criteria. The so-called upper castle (Oberburg) comprises a rectangular plaza as main square which is surrounded two rows of houses, and into the limestone a 57 m (187 ft) deep water well was carved. The lower castle (Unterburg) or lower town (Unterstadt) was probably built in the 14th century nestled at the castle's hill outside of the town wall. Therefore, it was not involved in the modernization of the upper castle in 1689.
Nowadays, the castle belongs to the Regensberg Castle Foundation. The round tower is still open to the public and offers a spectacular panoramic view of the surrounding region. In addition, information panels inside the tower relate the history of the small country town of Regensberg.
References:Rosenborg Palace was built in the period 1606-34 as Christian IV’s summerhouse just outside the ramparts of Copenhagen. Christian IV was very fond of the palace and often stayed at the castle when he resided in Copenhagen, and it was here that he died in 1648. After his death, the palace passed to his son King Frederik III, who together with his queen, Sophie Amalie, carried out several types of modernisation.
The last king who used the place as a residence was Frederik IV, and around 1720, Rosenborg was abandoned in favor of Frederiksborg Palace.Through the 1700s, considerable art treasures were collected at Rosenborg Castle, among other things items from the estates of deceased royalty and from Christiansborg after the fire there in 1794.
Soon the idea of a museum arose, and that was realised in 1833, which is The Royal Danish Collection’s official year of establishment.