The motte at Castletown marks the spot where Hugh de Lacy constructed a castle in 1182 for Robert de Bigarz, one of Strongbow’s men who had been granted the pre-Norman territory of Ui Buidhe (Oboy) sometime before 1176. This flat-topped conical mound rises 10 to 12 metres high, its summit spanning 6.5 metres across whilst its base measures approximately 30 metres in diameter. The structure remains remarkably intact, with steep sides to the west, north and east, though later additions include stone steps and a built-in seat on the southeast face. Traces of the original defensive fosse and external bank can still be spotted to the north where the modern road passes by.

The castle’s documented history reveals a succession of powerful medieval lords. After Robert de Bigarz, the lands passed to William de Cantilupe around 1245, then to John de Hastings in 1283. By 1348, the Earl of Pembroke was collecting 30 shillings annually from the burgesses of Castletown, indicating it had developed into a small borough with its own hundred court. Curiously, after this date, Castletown vanishes from the historical record until the late sixteenth century, leaving a gap of over two centuries in its story.

Today, the site shows signs of both preservation and adaptation. A cottage to the south and farm buildings to the southwest have caused some disturbance to the original earthworks. The area southeast of the motte, raised one to two metres above the surrounding fields, may represent the remains of a bailey; this space now forms the landscaped garden of Castletown House, enclosed by modern fencing. Despite these later alterations, the motte remains an evocative reminder of the Norman transformation of the Irish landscape and the strategic importance of this location in medieval Laois.