In the 1030s, a monk of Cluny named Rodulphus Glaber collected stories for a chronicle of his time entitled The Five Books of Histories. By his own account a wayward individual ill-suited to life as a monk, Glaber painted a vivid portrait of Christian society in northern Europe in the generation before the First Crusade. Among stories of warring kings, holy abbots, and vile heretics, Glaber penned several accounts of contemporary omens that portended terrible events, like the appearance of a dragon in the sky before the outbreak of a devastating civil war. One of these tales was the report of a ghostly army seen by a priest on the outskirts of the town of Tonnerre in Burgundy, the appearance of which foretold a terrible battle that took place there the following year.
In truth, we should remember very carefully that whenever prodigies are clearly revealed to people who are still alive whether by good or by evil spirits, it often happens that those who see them do not live for very long thereafter. We have learned many examples of this from which we will commend a few to memory, so that whenever it happens, people might show caution rather than be deceived. When Bruno was the bishop of Langres, there was a certain priest with a devout reputation named Frottier, who lived in the town of Tonnerre. One Sunday evening, as it grew dark and he was about to sit down to dinner, he went over to the windows of his house to relax for a bit. Looking out, he saw approaching from the north a host of horsemen, vast in number, marching westward arrayed as though for battle. After he watched them for some time, he grew anxious and summoned one of his servants to bear witness to this incredible sight. While he was calling out for the servant to come, the horsemen faded from view and suddenly vanished. The priest was overcome with such a great fright that he could hardly keep himself from crying. Thereafter he fell sick and in the same year, just as he had lived well, he died. Those who saw this were witnesses to the fact that he had been taken away from this life by the portent he had seen. For the very next year, Henry, the son of King Robert who ruled after his father, was moved by wrath and came to Tonnerre with a vast army, which resulted in an immense slaughter of men on both sides of the fight.