Built in 1192 during an English expedition from Leinster against Donnell O’Brien, king of North Munster, this castle was one of two constructed during the campaign, alongside Kilfeakle. The site overlooks a flat plain with the River Suir flowing roughly 500 metres to the west, offering commanding views to the north, east and west; a strategic position that would have been crucial for controlling the surrounding territory.

The motte itself was cleverly constructed atop a natural hill, with its summit measuring 12.6 metres north to south and 16.5 metres east to west. At the western end, the highest point, you can still trace the remains of a walled structure, now reduced to grass-covered walls standing less than a metre high. The northern side features a worn path leading to the summit, whilst the other sides remain practically sheer, making it an easily defensible position. Below, a roughly rectangular bailey extends approximately 57 by 59 metres, defined by a substantial stony bank that rises over 5 metres on its exterior face. Within this bailey, at the base of the motte, lie the foundations of what appears to be a rectangular structure, along with what early 20th-century antiquarian G.H. Orpen described as extensive stone foundations throughout the area.

The site’s history after its construction reveals the turbulent politics of medieval Ireland. In 1202, King John ordered the castle be delivered to William de Braose, only for it to be returned to Philip of Worcester in 1215. This grant was later confirmed by Henry III in 1225 to William of Worcester, Philip’s nephew. Today, the site forms part of a fascinating medieval landscape that includes a later tower house built within the bailey, another tower house to the northeast, and a church and graveyard, all testament to Knockgraffon’s enduring importance through the centuries.