A circular keep of five storeys, originally one of three towers in the curtain wall of a 13thc. Norman castle. The walls are up to twenty feet thick, with staircases and passages. On the south side of the second floor is an arch with Romanesque decoration on the inside.
The castle was begun by Theobald Walter c.1200 and completed in the first 20 years of the 13thc. It was burned in 1548. The top part of the tower was added in the 19thc.
Arch of embrasure leading to stair: a deep barrel vaulted niche with a modern window. The interior of the Window embrasure is decorated with a single row of lateral chevron on the face and on the soffit, carved point-to-point. The chevron roll is flanked by a narrow hollow. Decoration survives at the top and E side of the arch, while the W side and lower E side are missing. The carved stones are of sandstone, while the surrounding walls are of rubble masonry.
D. F. Gleeson and H. G. Leask, The Castle and Manor of Nenagh, Journal of the Royal Society of Antiquaries of Ireland, 66, 1936, 247-69.
H. G. Leask, Irish Castles: 1180-1310, Archaeological Journal, 93, 1936, 163-6.
H. G. Leask, Irish Castles and Castellated Houses, Dundalk, 1941, 43.
T. McNeill, Castles in Ireland, London, 1997, 28-31.