The present 13th-century and later stone castle of Conisbrough probably stands on a site first fortified with earthworks by King William's trusted supporter William of Warenne, soon after the Norman Conquest. Warenne's great-grandaughter married Hamelin Plantagenet-an illegitimate son of Geoffrey Plantagenet, Count of Anjou, and thus half-brother of King Henry II-who built the existing castle at some time between 1163 and 1202, probably during the 1180s.
The magnificent keep is very finely built of high-quality stone, and of very unusual and advanced design. Cylindrical keeps, stronger than earlier rectangular keeps with their vulnerable corners, were becoming fashionable in the late 12th century, but only Conisbrough's also features a ring of wedge-shaped buttresses, whose tops may have served as turrets for archers: four of the buttresses were hollow, containing a pigeon-loft, an oven, and cisterns for water, and another houses the tiny chapel off the lord's chamber on the third floor. The origins of this ingenious design are unknown: it is unique in Britain, though a smaller and much-ruined keep of similar type and date survives at Mortemer near Dieppe in northern France, a manor associated with the Warenne family. The curtain walls, plainly built soon after the keep, feature very early examples of semi-circular turrets, another advanced development in castle-building.
Conisbrough Castle hosted short royal visits from King John in 1201, and Edward II in 1322. From 1347 it became part of the estates of the royal Dukes of York: Richard 'of Conisbrough', Earl of Cambridge, younger son of the first duke, was probably born here, and after his execution for plotting against Henry V in 1415 it was occupied by his widow until her death in 1446. Thereafter however it gradually fell out of use, and by 1538 it was already ruinous and indefensible. Thus it avoided damage during the English Civil War.
Though the castle's famous appearance in Scott's Ivanhoe has made Conisbrough famous throughout the world, the events described there are of course purely fictitious. Perhaps because of its old name 'Cyningesburh'-a Saxon word meaning 'the king's fortress', perhaps referring to pre-Conquest earthworks round the church-or because of its unusual design, Scott wrongly believed the castle to be an ancient Anglo-Saxon building.
