Though circular on the outside, the interior reveals a square design with rooms measuring 6 metres across, spread over four storeys; the third level features distinctive vaulting. The castle’s substantial walls, reaching 4 metres at their thickest point, have endured centuries of transformation, including its conversion to a dwelling house by 1839 when Mr John Benson took residence there.

The castle’s history weaves through centuries of changing ownership and political upheaval. The ancient site, known as Rathsuird or Rathardasuird in the Book of Rights, served as a parish from 1253 to 1418. In 1583, John Browne of Knockmonye held the castle, which was then described as well-repaired with an iron door, a bawn, pigeon house and other buildings. Browne had acquired the entire property, including a third portion that had previously belonged to the FitzSimonds and carried an annual rent to Limerick city. The Desmond Survey valued the vill, castle and lands at two carucates or quarters yearly.

Through the turbulent 17th century, Rathurd passed through numerous hands; from Robert Anstey in 1589 to Nicholas Stritch in 1600, then to Nicholas Bourke and Philip Field in 1606, who held the castle with its fishery and other rights in fee. The Down Survey maps from this period depict it as a T or L-shaped house with prominent chimney stacks, accompanied by an orchard to the north. Following the Cromwellian period, grants were made to Captain J. Friend and Captain Winckworth in 1666. Today, remnants of an almost levelled rath can still be traced about 27 metres northwest of the castle, a testament to the site’s ancient origins and enduring significance in Limerick’s architectural heritage.