White Castle was established by the Normans in the wake of the invasion of England in 1066, to protect the route from Wales to Hereford. Possibly commissioned by William fitz Osbern, the Earl of Hereford, it comprised three large earthworks with timber defences. In 1135, a major Welsh revolt took place and in response King Stephen brought together White Castle and its sister fortifications of Grosmont and Skenfrith to form a lordship known as the 'Three Castles', which continued to play a role in defending the region from Welsh attack for several centuries.
King John gave the castle to a powerful royal official, Hubert de Burgh, in 1201. Over the next few decades, it passed back and forth between several owners, as Hubert, the rival de Braose family, and the Crown took control of the property. During this period, White Castle was substantially rebuilt, with stone curtain walls, mural towers and gatehouses. In 1267 it was granted to Edmund, the Earl of Lancaster, and remained in the hands of the earldom, and later duchy, of Lancaster until 1825.
Edward I's conquest of Wales in 1282 removed much of White Castle's military utility, and by the 16th century it had fallen into disuse and ruin.
The castle is made up of a central inner ward, a crescent-shaped hornwork to the south, and an outer ward to the north, with its stonework constructed from red sandstone. The outer ward was originally much larger, extending around the castle further to the east, but only limited traces of these earthworks survive. It is now entered from the north-east although, prior to the 13th century, the castle 's entrance was originally on the south side. The historian Paul Remfry considers the castle to be 'a masterpiece of military engineering' for the period.
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.