After the le Bruns, Rathdown passed to the Fitzgerald family (Earls of Kildare). In 1534, the proprietor was Richard Fitzgerald, and Rathdown contained a castle, 20 messuages (houses), 248 acres, a water-mill, and a river called the Water of Rathdown, as well as a crykka (creek).
The castle and lands were later in 1536 granted by Henry VIII to Peter Talbot. The Talbots retained Rathdown for over one hundred years. They defended Rathdown against attacks from the O’Byrne clan during this time. Following the rebellion and wars of 1640, the Talbots lost Rathdown. The last Talbot at Rathdown was Bernard Talbot.
The Down Survey of 1657 describes the castle of Rathdown as ruined, and observes that the barony of Rathdown was not very well inhabited, occasioned “partly by the roughness of the country and partly by the destruction of the ancient Irish inhabitants during the late wars”.
There is no disputing Rathdown’s influence and importance in medieval times. Eventually, decline, abandonment and destruction followed in the 1600’s, leaving St. Crispin’s Cell and Captain Tarrant’s farmhouse as the only visible evidence now of past glory.
Smal, Chris (1993), Ancient Rathdown and St. Crispin’s Cell, a uniquely historic landscape. Friends of Historic Rathdown, Greystones.