Wiston Castle (Welsh: Castell Cas-wis) is a motte and bailey castle in the Pembrokeshire village of Wiston in south west Wales and is one of the best examples of its type in Wales. The castle and village were founded by Wizo, a Flemish settler who was granted the land by Henry I of England after he had wrested control from the previous owner, Arnulf de Montgomery (who was in revolt against Henry). The castle was captured by the Welsh on several occasions but on each occasion it was retaken. It was abandoned during the thirteenth century when the then owner moved to nearby Picton Castle.

The castle is situated opposite St Mary Magdalene Church and there are approximately 50 steps leading up to it. It is in the care of Cadw and is a Grade I listed building and a Scheduled Monument.

Until the late eleventh century, this part of southwestern Wales was part of the Welsh state of Deheubarth. The exact administrative structure of Dehubarth is unclear, but it may have been something of an amalgamation of sub-kingdoms, there being a Lord of Dyfed (named Cadifor) in this period, from the earlier line of rulers of Dyfed. Under King William I, Rhys ap Tewdwr, the ruling king of Deheubarth, accepted William's suzerainty, and enjoyed support as a loyal vassal.

In 1088, however, when William died, Rhys, believing his vassalage to be for William's life only, attacked Worcester (in alliance with other powerful rebel vassals); in theory, treason made his lands forfeit. In 1092, Deheubarth was internally destabilised when Cadifor died, and his sons refused to accept the authority of Rhys ap Tewdwr, instead calling for a rival to assume the throne. Though Rhys managed to suppress the rebellion, he was killed in the following year, in the Battle of Brecon, while attacking Bernard de Neufmarche (the husband of Nest, granddaughter of the previous - and only - Welsh King of Wales).

Following Rhys' death, the king's agents immediately seized much of Deheubarth; the west of Dyfed was seized by Arnulf de Montgomery, while the north and eastern parts were seized by Normans sailing from Devon - Martin de Turribus and William fitz Baldwin (sheriff of Devon, and son of the previous such sheriff, Baldwin FitzGilbert) respectively. At the same time Normans also took much of the rest of South Wales (although according to an old Welsh legend, reported by the Tudor antiquarian John Leland, this conquest east of Deheubarth was at the request of Cadifor's surviving brother/son, Einion). South western Dyfed, including the land in which Wiston was later sited, became a Marcher Lordship under Arnulf's rule; Arnulf built a castle at Pembroke from which to rule the land (the Lordship becoming of Pembroke as a result).

In 1102, following the death of King William's successor William Rufus, the Kingship passed to his brother, Henry I, but again many powerful vassals - including Arnulf de Montgomery - rebelled in favour of Henry's elder brother (Robert Curthose). Henry declared Arnulf's lands forfeit, and kept Arnulf's former Marcher Lordship for himself. Six years later, in 1108, Flanders, the lands of Henry's mother, suffered catastrophic flooding, and many refugees sought help from Henry. Henry settled them in his newly acquired lordship, particularly Roose (aka Haverford) and Dungleddy. The Flemings maintained their culture and were an identifiable group for at least a century; indeed the distinction between the Fleming-populated areas and the rest of Wales still leaves a strong mark in the local DNA.

The Flemish leader in Dungleddy, a man named Wizo, built a castle to control his lands; it was effective in controlling Dungleddy. Around the castle a settlement arose, named after Wizo - Wiston (Old Flemish/Saxon for Wizo's enclosure/town) - hence the castle came to be called Wiston Castle. Wizo parcelled out some of his lands to lesser Flemings, one of whom, in 1130, was Wizo's son, Walter fitz-Wizo. Wizo was later to carry out a similar colonisation in Lanarkshire in Scotland. ^{[citation needed]}

In 1147, the Welsh led by Hywel ab Owain captured Wiston, now under control of Walter, but the Flemings soon got it back. Towards the end of the century, Dungleddy (and the Lordship of Pembroke in general) came under pressure from the sons of Lord Rhys, who were trying to aid their father to re-establish Deheubarth. In 1193, Hywel the Saxon (son of Lord Rhys) attacked the Flemings, captured Wiston Castle, and took Wizo's other son, Philip, captive (along with Philip's wife and sons). Philip had only just recently donated lands in Dungelly to the Knights Hospitaller. It took two years before the Flemings were able to recover Wiston Castle (and hence governance of Dungelly).