How did Lorenzo Valla show that the Donation of Constantine was a forgery?

In 1440, the Italian humanist Lorenzo Valla utilized the methods of philology to expose the Donation of Constantine as a forgery.123

While the document purported to be a 4th-century decree from the Roman emperor Constantine the Great granting the papacy vast territorial and temporal power, Valla’s analysis focused on the text's linguistic evidence. He demonstrated that the Latin style and diction used by the anonymous author were characteristic of the 8th century rather than the 4th century. By identifying these anachronisms, Valla proved that the document could not have originated from the time of Constantine.132

This work, titled Declamatio, served as a significant triumph of Renaissance scholarship, as it effectively undermined the historical foundation of papal claims to secular authority in the West. Valla’s approach highlighted the power of critical linguistic analysis to challenge long-standing traditions and established authorities.23