This four-storey tower house, originally built as a gatehouse for a polygonal castle enclosure, tells a story spanning nearly 850 years. The castle complex, stretching between Nugent Street to the west and Cox’s Lane to the east, was likely constructed by Strongbow himself in the early 1170s, though some historians credit William Marshall with its construction before 1185. The original fortification consisted of a curtain-walled polygonal enclosure covering roughly 0.43 hectares, complete with four defensive towers and possibly a motte at its southern angle.

Today, visitors can still trace three sides of the original polygonal walls; northwest, northeast and southeast; along with the converted gatehouse and the lower courses of two mural towers. The gatehouse itself is a fascinating study in medieval adaptation, built from rubble limestone with a distinctive base batter on three sides. Its ground floor entrance, now filled with a post-medieval window, once required a timber gangway due to the three-metre difference in ground level between the enclosed castle ward and the outside. Inside, a complex arrangement of stairs, chambers and defensive features reveals its military purpose, including twin-light windows, a garderobe, and intramural chambers that provided both living quarters and defensive positions.

The castle’s history reads like a roll call of medieval Irish conflicts. It weathered a three-day assault by Edward Bruce in 1316, underwent significant repairs between 1297 and 1299 when new kitchens, a bakehouse and a well were added, and by 1331 boasted four towers, a chapel and kitchen facilities. During the 15th century, the Anglo-Norman gatehouse was converted into a tower house, with the original curtain walls serving as its bawn. While much of the castle has been lost to time, including the ‘Old Tower’ marked on an 18th-century map and parts now incorporated into Graham’s Bakery on Market Square, what remains offers a tangible connection to Kildare’s strategic importance during the Anglo-Norman conquest of Ireland.