The first castle in Neath was located west of the river near the Roman fort of Nidum, and was a timber fortification in a motte and bailey structure. When Richard de Grenville founded Neath Abbey close by, he abandoned this original castle, and it may have been used by the monks as a source of building material.
A second castle on the opposite bank of the river, in what is now the centre of the town, is first documented in 1183; shortly afterwards, William de Cogan, son of Miles de Cogan, was appointed constable. This second castle was built by Gilbert de Clare, 5th Earl of Gloucester. During the 13th century, being a Norman stronghold, it was subject to attack by the Welsh, notably by Llywelyn the Great, who captured it in 1231 with help from a local Welsh lord, Morgan Gam. Following this, it was substantially rebuilt by Richard de Clare, 6th Earl of Gloucester, Gilbert's son.
It was taken again, and this time destroyed, by Humphrey de Bohun, 4th Earl of Hereford, in 1321, during the rebellion against King Edward II of England. Its owner, Hugh Despenser the Younger (who had gained the lordship through his marriage to the heiress Eleanor de Clare), rebuilt it, possibly with the addition of a gatehouse. In 1376, one Roger Kyngot was the constable, and the castle was rebuilt in stone in 1377; that is probably when the great gatehouse was built, which is the main surviving feature. The castle was in use until the 17th century, and has been a recreational area for the town since the 18th century.
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.