The Bonn Minster (Bonner Münster) is one of Germany's oldest churches, having been built between the 11th and 13th centuries. At one point the church served as the cathedral for the Archbishopric of Cologne.
Castra Bonnensia was a fortress on the site of current Bonn built by the Romans in the 1st century AD. It survived the breakup of the Roman Empire as a civilian settlement, and in the 9th century it became the Frankish town of Bonnburg.
Around 235 AD, two Christian Roman soldiers stationed in Castra Bonnensia, Cassius and Florentius, were martyred for their faith. Tradition has it that a small memorial shrine was built over their graves in the 4th century by St. Helen, mother of Constantine. There is no surviving evidence of this first structure, but archaeological excavations have shown that the basilica stands on the site of a Roman temple and necropolis.
The original memorial hall was expanded into a larger church in the 6th and 7th centuries, and many people were buried near the martyrs inside and outside the building. Further extensions were carried out in the 8th century.
Around 1050 the church was demolished and construction began on the present Romanesque building, which dates from the 11th to 13th centuries. By the end of this period Bonn had grown in importance, becoming the capital of the Electorate and Archbishopric of Cologne, which was then a sovereign state. The new basilica appeared in the city's coat of arms. In 1643, Cassius and Florentius were officially declared the patron saints of the city of Bonn.
The basilica suffered significant damage in 1583-89, 1689, and in World War II, but each time it was fully restored. In 1956, the Bonner Münster was granted the status of Papal Minor Basilica.
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.