Peter the Venerable, the ninth abbot of Cluny, who ruled the great Burgundian monastery from 1122 until his death in 1156, understood the didactic potential of ghost stories. In a treatise on miracles written in the 1140s, he related several tales of hauntings that took place at Cluny to warn his audience about the punishments awaiting sinners in the afterlife and to promote the power of Cluniac prayer to relieve their suffering and to speed their souls to heaven. These kinds of stories were not subtle. Time and again, the spirits of the dead appeared to Cluniac monks to beseech their prayers to remedy the otherworldly pain that they had earned for a host of mundane sins: a nobleman's love of plundering, a bishop's fondness for laughter. The prayers of the community never failed these sinners, whose apparitions almost always returned to the abbey one last time to give the brethren thanks before departing for heaven.

It should not surprise us, then, that the earliest account of Peter the Venerable's life and miracles featured a ghost story. Composed in the late twelfth century by Rodulphus de Sully, the twelfth abbot of Cluny (1173–1176), this short vita survives in no medieval manuscripts; we owe its preservation to the industry of the Maurists, who copied it in the eighteenth century. The ghost story told by Rodulphus de Sully was unusual because the spectre in question was a king of England, none other than King Henry I (1100–35). According to this miracle, the ghost of the monarch appeared upon a black horse ‘as though alive (quasi vivus)’ to one of his own soldiers in England. He was accompanied by a great multitude of mounted knights. ‘Are you not my lord?’ asked the soldier in amazement, ‘Are you not dead?’ ‘Truly, I am dead,’ replied the spectre, ‘and my death would have been eternal, if Lord Peter, the abbot of Cluny, with his brethren had not come to my aid.’ The ghost of Henry I ordered the soldier to make haste to Lewes priory, a Cluniac dependency in Southover, East Sussex. He was told to relate the story of the ghost to the brethren who lived there, and bid them to send a letter to Abbot Peter at Cluny requesting prayers of intercession on his behalf.