The Bishop's Castle or Palace is the only surviving residence of the medieval clergy of Llandaff. It consists of remains of a sub-rectangular enclosure, circa 52m north-west to south-east by 40m, that is defined by ruinous masonry curtain walls, towers and a monumental gatehouse at the western angle, facing the approach from the Cathedral.

The castle is shown complete on John Speed's plan of 1610, with the gatehouse and four other towers, so it was presumably dismantled at the time of the Civil War. A photograph of circa 1860 shows that it has received only a small amount of repair and consolidation since that date (mainly in 1971). The castle was a part of the Bishop's Palace garden while he was resident (1850-1939) in what is now the Cathedral School. It was given to the City of Cardiff in 1971, was repaired by them, and was opened as a public garden in 1972. The castle is a grade I listed building because of its importance as a medieval Bishop's Castle that was probably first constructed by William de Broase (Bishop 1266-87) during the thirteenth century, and is still remarkably well preserved.

Sources:
The Royal Commission on the Ancient and Historical Monuments of Wales (2000): An Inventory of the Ancient Monuments in Glamorgan Volume III - Part b, Medieval Secular Monuments, the Later Castles, From 1217 to the Present. LM2 - Bishop's Castle, Llandaf.

Cadw Listed Buildings Record number 13718, Cadw SAM number GM073

Claire Parry, RCAHMW, 17 August 2011