What visitors see today is actually three distinct structures melded into one: a probable 12th century earthwork motte, a 13th century Anglo-Norman stone castle, and a late 16th to 17th century fortified house. The site’s strategic position, 470 feet above sea level overlooking bogland to the north and east, made it a coveted stronghold throughout its tumultuous history.

The castle’s story begins with Meiler FitzHenry receiving the Barony of Carbury, though it later passed to William Marshal and then to the de Bermingham family, who built the first masonry castle sometime before 1234. The de Berminghams left their mark on history in the darkest way possible; in 1305, Peter de Bermingham orchestrated the massacre of approximately 30 leading O’Connors of Offaly and their followers within these walls, sparking widespread warfare between the Anglo-Normans and the Irish. The castle changed hands repeatedly over the centuries, suffering demolition in 1475 and again in 1556 when it was plundered and burnt. In 1562, ownership passed to the Colley family, ancestors of the Duke of Wellington, who held it until its final abandonment in 1774.

Today’s ruins reveal the castle’s architectural evolution beautifully. The original motte, a steep-sided earthwork standing about 5 metres high, may have initially supported a timber castle before being repurposed as a bailey for the stone fortress. The 13th century masonry castle survives as thick rubble walls rising three storeys, later enhanced with barrel vaults inserted in the late 13th century. The structure was subsequently extended northward and eastward, gaining Jacobean-style chimneys and mullioned windows that speak to its transformation into a more comfortable, though still fortified, residence. Scattered remnants of mortared masonry, a possible gun platform, and evidence of an adjacent quarry that likely provided building stone whilst enhancing the site’s defences, all contribute to this remarkable palimpsest of Irish castle architecture.