This Norman motte and bailey castle consists of a large circular mound with steep sides and a flat summit. The motte measures approximately 76 metres north to south and 69 metres east to west at its base, rising to a height of just over 11 metres. The summit platform, where a wooden tower would have once stood, spans about 21 metres across.

Surrounding the base of the motte is a wide, shallow defensive ditch or fosse, reaching its maximum width of 11.4 metres on the western side and plunging to a depth of 3 metres. This water-filled moat would have served as the first line of defence against attackers attempting to scale the earthen mound. The engineering required to construct such a substantial earthwork demonstrates the considerable resources and labour the Normans could command in medieval Ireland.

To the west of the motte lies a crescent-shaped bailey, an enclosed courtyard that would have contained the domestic buildings, stables, workshops and stores necessary for daily life in a Norman castle. This bailey extends 55 metres from east to west and nearly 30 metres from north to south, defined by an earthen scarp on most sides. Only on its eastern edge does the fosse separate it from the main motte, creating a formidable defensive complex that once controlled this strategic position along the Liffey valley.