White Castle originally comprised earthwork and timber defences erected in the manor of Llantilio Crossenny by the Normans in the wake of the Norman Conquest in order to protect the communication routes between Hereford and Wales, forming a triangle of fortifications together with Grosmont Castle (NPRN 93388) and Skenfrith Castle (NPRN 93431).
The castle was rebuilt in its characteristic white stone during the twelfth century, with a stone curtain and square keep. During the thirteenth century further fortifications were carried out in response to the rise of Llewellyn ap Gruffudd, and the castle took the shape that survives today, with a twin-towered gatehouse and series of four D-shaped towers, equipped with distinctive cross-shaped arrow loops. The earthwork defence to the north of the castle was enclosed within a stone curtain wall with circular towers and a gatehouse, while the keep and gatehouse to the south were demolished and replaced with a postern gate and battery of further loops.
In contrast to Grosmont and Skenfrith, White Castle lacked high-status domestic accommodation to suit the nobility, indicating that it served more as a military garrison than a seat of power. Despite repair work carried out during the fifteenth century, by 1538 it was entirely abandoned, and remained disused until it came into State care in 1922.
Source: Knight, J.K. 2000. The Three Castles: Cadw Guide (Second Edition)
K Steele, RCAHMW, 4 November 2008