For Centuries, Few Questioned the Legitimacy of This Obviously Fake Document
After the Donation of Constantine was forged, it was stashed away and forgotten for hundreds of years. Then Pope Leo IX dusted it off in the mid-eleventh century, and cited it to assert his authority over secular rulers. Surprisingly, the fake document was widely accepted as authentic, and few questioned its legitimacy. For centuries thereafter, the Donation carried significant weight whenever a pope pulled it out to figuratively wave in the face of secular rulers. It was not until the Renaissance and the spread of secular humanism that its authenticity was finally challenged.

With the revival of Classical scholarship and textual criticism, scholars took a fresh look at the document. It quickly became clear that the text could not have dated to the days of Constantine the Great and Pope Sylvester I. The document used language and terms that did not exist in the fourth century, but only came into use hundreds of years later. It also contained dating errors that a person who wrote at the time could not have made. The popes did not officially renounce the Donation. From the mid-fifteenth century, however, they ceased to reference it in their Bulls and pronouncements.