This large "keepless" fortress is often claimed to be the only surviving early medieval castle of an Irish ruler. It was built in the 1290s and has a roughly square plan, with enormous asymmetrical polygonal corner towers and a gateway in the eastern curtain, flanked by comparatively small projecting turrets. However, residential apartments in the upper floors of the towers appear quite sophisticated in their design, indicating that Norman rather than Irish architects were employed. Indeed, the oft-repeated claim that this castle was built by the O'Connors of the Royal House of Connaught is difficult to sustain, especially as Irish chiefs of this period had no use for such fortresses. Furthermore, in the 1333 inquisition of the Earldom of Ulster, a hundred court is recorded at Ballintober. It is likely the builder was William de Burgo, and no doubt the castle's large area was intended to permit an Anglo-Norman settlement within its walls. The northern towers are higher than the others as they were rebuilt and repaired in 1627. Outside the walls extra protection was afforded by a wide water-filled moat. The castle fell into the hands of the O'Connors in the 14th century and remained in their possession for many centuries, being the chief seat of the O'Connor Don from 1385 until 1652. In 1598 it was surrendered to Red Hugh O'Donnell, who attacked it with cannon, breached its walls and forced Hugh O'Connor Don to recant his allegiance to the Crown. In 1641 it became a centre of Catholic resistance with the result that it was confiscated in 1652. The O'Connors regained possession in 1677 and remained in residence until 1701, when it was abandoned.
17.5 km (11 miles) NW of Roscommon off the Tulsk Road. NGR: M 729748.