After the death of Charlemagne (in 814 AD), a legend emerged alleging that the ruler had committed some kind of "unspeakable sin."
The legend first appeared in print in a 10th-century work called The Life of St. Giles
. According to this work, Charlemagne had sought out St. Giles to ask the saint to pray for him because he had committed a sin so terrible that he had never been able to confess it properly. Giles reportedly agreed to pray for the king, even though Charlemagne didn't tell him what the sin was.
The fact that the unspeakable sin wasn't disclosed whet the imaginations of later medieval writers, creating a minor genre devoted to exploring what the sin was. Details from Charlemagne: Father of Europe
(2022) by Philip Daileader.
Until the 13th century, authors equivocated when speaking of the unspeakable sin alluded to in the Life of St. Giles. Some authors continued to dodge the issue in the centuries to come, but others did not. They made shocking accusations against Charlemagne and committed them to writing. Perhaps the accusations themselves were invented in the 13th century, or perhaps such claims had long circulated awaiting the moment when authors finally mustered the courage to write them down. Be that as it may, authors offered two different identifications of Charlemagne's unspeakable sin. Some authors identified Charlemagne's unspeakable sin as incest. Specifically, they claimed that incestuous relations between Charlemagne and his sister, Gisela, had in turn resulted in Gisela giving birth to Roland, the hero of the Song of Roland.
The allegation of an incestuous relationship between Charlemagne and Gisela appears in the Karlamagnus Saga, a 13th century account of Charlemagne's life written in Norse. From there, the incest claim is then taken up by a number of different texts, especially French texts.
Other authors identified Charlemagne's unspeakable sin as necrophilia. That claim appears in a 14th century German poem about Charlemagne, "Karl Meinet," and the idea was then taken up in a number of 14th and 15th century German chronicles and treatises.
Specifically, someone had hexed Charlemagne by placing a charmed ring under the tongue of his dead wife. The ring caused Charlemagne to become infatuated with the wife and to continue the relations they had had while she was alive. When a bishop discovered the ring and removed it from the dead wife's mouth, Charlemagne became infatuated with the bishop. The bishop tossed the ring into a swamp, and Charlemagne became infatuated with the swamp, building a palace and dwelling there. To be clear, none of this is true...
One can only speculate as to why stories arose alleging that Charlemagne was guilty of incest or necrophilia, and why those stories gained a significant and distinguished audience. These stories did not emerge in or remain confined to a specific geographical milieu. They do not seem to have been concocted to achieve any specific political outcome. Perhaps they emerged primarily as a reaction against the overblown praise that Charlemagne received in other works. The bigger they come, the harder they fall.
Detail from a Flemish altarpiece (ca. 1400) showing Charlemagne asking St. Giles to pray for him.
Source: Victoria and Albert Museum