The medieval world had its own ‘deepfakes’ – church officials cited a fake imperial decree for centuries

At least 10 medieval popes cited the “Donation of Constantine,” a document claiming Emperor Constantine I granted Pope Sylvester I authority over Rome and the Western Roman Empire in the early 300s, to justify expanding papal control across Italy. No document referencing this supposed transfer exists before the eighth century, and Pope Adrian I first invoked it in a 778 letter to Charlemagne seeking territorial concessions.

The forgery persisted through the 1054 East-West church split, when Pope Leo IX invoked it by name, and was still influential enough by the 1300s that Dante placed a pope in hell for the temporal greed the Donation had encouraged. In 1433, Cardinal Nicholas of Cusa was the first to publicly suggest it was fake, and in the following years Lorenzo Valla, an Italian humanist priest, methodically proved the forgery using anachronistic language and absent contemporary sources.

Valla concluded the document was likely fabricated by a Roman cleric between 750 and 850, and accused the church of maintaining the deceit for centuries by insisting on its authenticity.

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