Built in the latter half of the 13th century by the Anglo-Norman Prendergast family, who later adopted the Irish name MacMorris or MacMorys, this castle served as a stronghold for centuries of changing ownership. The MacMorris clan held the castle through the 16th century, with Walter oge MacMorris recorded as chief in 1574, succeeded by Richard Mac Morys who gained English title to the property during the Composition of Connacht in 1585. That same December, Richard transferred the castle to Francis Barkley, Marshal of Connacht, beginning a chain of ownership that would eventually see the property pass to John Moore, whose claim was confirmed by King James I in 1607. The Moore family retained possession until the late 19th century.

Today, visitors to Brees will find a substantial ruin consisting of a sub-rectangular enclosure measuring roughly 16 metres east to west and 24 metres north to south, its curtain walls following the natural contours of the rocky knoll. The defensive walls, now reduced to sod-covered rubble banks on their inner faces, still rise 2 to 3 metres high externally where they were cleverly built onto the scarped slopes of the knoll, making use of the natural defences provided by the steep terrain. Remnants of the original construction can be spotted at various points; a section of intact wall face at the north-northeast shows roughly coursed limestone with traces of a base batter, whilst similar remnants survive at the southern section. The southeastern corner hints at what may have been a gateway or entrance tower, marked by a slight projection in the wall and broken masonry showing traces of vaulting.

Within the castle’s interior, archaeological traces reveal the ghost of its former buildings. An east to west wall runs about 5 metres south of the northern curtain wall, with fainter wall footings extending south-southeast, likely preserving the outline of a rectangular building or hall that once stood against the eastern curtain wall. Large chunks of displaced masonry scattered on the southern and southwestern slopes bear witness to the castle’s gradual decay, whilst the surrounding landscape shows signs of its working past through relict cultivation ridges and old quarrying sites dotting the knoll and ridge.