The substantial motte rises 12 metres above the flood plain, with its top measuring 39 by 20 metres and its base spanning 66 by 48 metres. To the east lies a bailey enclosed by reduced earthen banks, best preserved at the western end where the southern bank still stands 4 metres high above the plain. This fortification was likely built by William Marshall, who died in 1219 and is credited with founding the town. Marshall probably had his steward, possibly Geoffrey Fitz Robert who also built the motte at Kells, supervise the construction, which cleverly incorporated a natural ridge that was then augmented to create the imposing earthwork.

Historical records paint a vivid picture of the castle’s medieval heyday. In 1247, the castle and town passed to Isabella Marshal’s son, Richard de Clare, Earl of Gloucester and Hertford. A detailed survey from 1307, following the death of Joan, Countess of Gloucester and Hertford, describes “a castle in which there was a hall constructed of wood, with wooden shingles, a stone chamber, a kitchen, and other wooden chambers.” By the 16th century, the area around the motte had been transformed into gardens, as evidenced by a 1539 lease from the Earl of Ormond granting Rose Hedyn and Piers Herforde’s children two houses, a garden by the motte, and 17½ acres of arable land. The tenants’ feudal obligations included providing two ‘ryppen hokes’, two ‘wotghe’ hens, and two men to maintain the millpond.

A 2002 geophysical and topographical survey revealed fascinating details about the site’s medieval layout. The survey detected anomalies corresponding to medieval buildings on the motte, including what appears to be a hall measuring approximately 17 by 18.5 metres, as well as structures within the bailey. North of the bailey, about 40 to 50 metres away, the survey identified what may be a kiln about 7 metres wide and a furnace approximately 5 metres wide. Today, visitors can still trace the outline of the bailey’s defensive banks, particularly where the northern bank curves near an ESB pole, and observe the smaller triangular mound immediately west of the motte; a remnant of the natural ridge left after construction. From the motte’s summit, despite the overgrowth, one can still enjoy commanding views in all directions, including eastward to the Augustinian friary, much as medieval sentries would have done centuries ago.