Set in a pretty valley within a protective bend of the River Clun, Clun Castle is at first glance an unusual fortification when compared to many castles of the period. Built in an area often referred to as the Welsh Marches, Clun Castle was at the centre of a Marcher lordship known as the Honour of Clun. Controlled originally by Anglo-Saxons and experiencing frequent Welsh incursions, the Norman invaders loyal to William the Conqueror would have found the area rather troublesome. Therefore, a method was needed to subjugate the local population, and the Norman motte and bailey castle would have provided the answer.

Picot de Say is believed to have been the first marcher lord to construct a timber castle on the site, and the natural rock formations would have been easily fashioned to provide the high mound required for the central keep and also the inner bailey of Clun Castle. There are two baileys at Clun Castle, the larger inner bailey to the south, and a smaller outer bailey to the east where the modern bowling green resides. A rock gully provided a means of separating the southern inner bailey from the motte, and access to this would have been via a drawbridge, the buttresses of which can still be made out.

Earliest records of Clun Castle are in 1140. In 1155 the castle passed to the Fitzalan family when Isabel, Picot de Say's great granddaughter, married William Fitzalan, Lord of Owestry. In 1196 the timber castle was captured and burnt by Prince Rhys of South Wales after a long siege. At the time of the Magna Carter disputes, Clun Castle is known to have fallen to King John.

Further Welsh incursions occurred in 1214, when Prince Llewelyn ap Lorweeth captured and burnt the castle, and again on his return in 1234 - this time he failed to take the castle, but burnt the town instead. It is not known when the castle was re-built in stone but it would seem reasonable to assume that it was at some time after the 1196 or 1214 sacking. The fact that Clun Castle survived the third Welsh attack in 1234 also adds weight to this theory.

An inventory was made of the castle in 1272, which highlighted some repairs that were needed, but by the time King Edward I had subdued Wales in 1282, the strategic importance of Clun Castle had lost its significance.

In 1289 John Fitzalan III was created Earl of Arundel and from that time forward the Lords of Clun appear to have largely neglected their Marcher estates for those of Arundel Castle. However, the hunting in Clun Forest was known to have been very good and a hunting lodge would have been required to provide accommodation for the lord and his party. During this period - early to mid 14th century - the unusual great tower is believed to have been built. This great square tower survives almost to its full height, but has lost much of its southern wall. What makes this 'Keep' so unusual is the fact that it is let into the northern side of the motte, rather than being constructed on top. It comprises a basement and three floors, each level becoming more grand, as evidenced by the surviving masonry.

This type of arrangement could not have been for military use, as the great tower would have proved much easier to undermine and attack than its traditional counterpart. Two semi-circular towers also survive within the western curtain wall but, again, the architecture suggests these were more for effect than defence. On the low-lying ground to the west, there is evidence of formal gardens and pavilions. This would further suggest that Clun Castle was being used as a grand hunting lodge, rather than a fortified home and administrative centre.

Clun Castle was attacked c1400 by Owain Glyndwr, but by this time it was not the defensive obstacle that it once would have been. Over the next two centuries Clun Castle slipped into obscurity and, by the time of the English Civil War in the mid 17th century, the castle was in such a dilapidated state even the local church was able to provide a better defensive position.