This Anglo-Norman earthwork takes the form of a raised oval mound, measuring roughly 22 metres east to west and 25 metres north to south, rising to a height of 4.8 metres at its northern end. The fortification retains some of its original defensive features, including a low earthen bank about 2.2 metres wide and 1.8 metres high along the northern and western sides, whilst a flat-bottomed fosse, or defensive ditch, approximately 4.8 metres wide, guards the eastern and northern approaches.

The site has suffered considerable damage over the centuries, with quarrying activities destroying much of the eastern and southern portions of the motte. Historical records from O’Hanlon and O’Leary’s 1907 work make reference to a rath at this location, though the structure clearly represents Norman military architecture rather than an earlier Irish ringfort. The strategic importance of this position becomes apparent when considering its location directly across from Ardree in County Kildare, which historian G.H. Orpen identified as a thriving Anglo-Norman manor in the medieval period.

Archaeological evidence supports the site’s Anglo-Norman origins; pottery fragments typical of the period have been discovered on the motte’s summit. These finds, combined with the castle’s proximity to the established manor at Ardree, suggest Dunbrin Lower played a role in the Norman colonisation and control of this region during the medieval period. The motte would have originally supported a wooden tower or keep, serving as both a defensive stronghold and a visible symbol of Norman authority over the surrounding landscape.