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:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.