These humble remnants, little more than loosely piled rubble, give few hints about the fortress that commanded this strategic position between the river to the north and the uplands to the south. The castle’s destruction was so complete that visitors today would struggle to recognise it as the site of a once-important stronghold without prior knowledge.

The most significant surviving feature is a wide fosse, or defensive ditch, measuring three metres across and half a metre deep, which curves along the southern and eastern edges of the site. This earthwork likely defined the boundaries of a bailey; the outer courtyard that would have contained workshops, stables, and accommodation for the castle’s garrison and servants. Such features were essential components of medieval castle design, providing both defensive capabilities and practical space for the daily operations of a functioning fortress.

The O’Carroll clan, who gave the castle its name, were powerful Gaelic lords who controlled much of what is now County Offaly from the 14th to the 17th centuries. Their various castles and tower houses throughout the region served as centres of administration and symbols of their authority. While historical records from O’Flanagan’s 1933 work reference this particular castle, the exact circumstances of its destruction remain unclear; whether it fell during the turbulent centuries of Anglo-Norman expansion, the Cromwellian conquest, or simply succumbed to neglect and time.