Shortly after the Romans founded Cologne in 50 AD, they built a wall around the city. The wall was first expanded in the tenth century, and again in 1106, but due to the continuing growth of the city a new, 7 meters high wall was built in the twelfth and thirteenth centuries.
The most important of the twelve gates that gave entrance to Cologne was the west gate, known as the Hahnentor. After their coronation in Aachen, German kings arrived in Cologne through this gate to revere the shrine of the Three Magi in the Cologne cathedral. The gate was built between 1235 and 1240 and was probably named after a citizen named Hageno, who owned the nearby land.
The Hahnentorburg has two semi-circular, crenellated towers. The city's coat of arms is depicted above the entrance. The tower was restored in 1890 by the city architect Josef Stubben; a memorial plaque commemorates the architect's construction of Neustadt (new city) between 1881 and 1898 outside the former city walls. The tower was severely damaged during the Second World War, but was later reconstructed.
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.