Investigation
During the Middle Ages, the Donation was widely accepted as authentic, although the Emperor Otto III did possibly raise suspicions of the document "in letters of gold" as a forgery, in making a gift to the See of Rome. It was not until the mid 15th century, with the revival of Classical scholarship and textual criticism, that humanists, and eventually the bureaucracy of the Church, began to realize that the document could not possibly be genuine. Cardinal Nicholas of Cusa declared it to be a forgery and spoke of it as an apocryphal work. Later, the Catholic priest Lorenzo Valla, in De falso credita et ementita Constantini donatione declamatio, proved the forgery with certainty. This was the first instance of modern, scientific diplomatics. Independently of both Cusa and Valla, Reginald Pecocke, Bishop of Chichester (1450–57), reached a similar conclusion. Among the indications that the Donation must be a fake are its language and the fact that, while certain imperial-era formulas are used in the text, some of the Latin in the document could not have been written in the fourth century; anachronistic terms such as "fief" were used. Also, the purported date of the document is inconsistent with the content of the document itself, as it refers both to the fourth consulate of Constantine (315) as well as the consulate of Gallicanus (317).
Pope Pius II wrote a tract in 1453, five years before becoming Pope, to show that, though the Donation was a forgery, the Church owed its lands to Charlemagne and its powers of the keys to Peter; he did not publish it, however.
Although the bulls of Nicholas V and his successors made no further mention of the Donation, even when partitioning the New World, Valla's treatise was placed on the list of banned books in the mid-sixteenth century. The Donation continued to be tacitly accepted as authentic until Caesar Baronius in his "Annales Ecclesiastici" (published 1588–1607) admitted that it was a forgery, after which it was almost universally accepted as such. Some continued to argue for its authenticity; nearly a century after "Annales Ecclesiastici", Christian Wolff still alluded to the Donation as undisputed fact.
More recently, scholars have further demonstrated that other elements, such as Sylvester's curing of Constantine, are legends which originated at a later time. Wolfram Setz, a recent editor of Valla's work, has affirmed that at the time of Valla's refutation, Constantine's alleged "donation" was no longer a matter of contemporary relevance in political theory and that it simply provided an opportunity for an exercise in legal rhetoric.
Contemporary opponents of papal powers in Italy emphasized the primacy of civil law and civil jurisdiction, now firmly embodied once again in the Justinian Corpus Juris Civilis. The Florentine chronicler Giovanni Cavalcanti reported that, in the very year of Valla's treatise, Filippo Maria Visconti, Duke of Milan, made diplomatic overtures toward Cosimo de' Medici in Florence, proposing an alliance against the Pope. In reference to the Donation, Visconti wrote: "It so happens that even if Constantine consigned to Sylvester so many and such rich gifts—which is doubtful, because such a privilege can nowhere be found—he could only have granted them for his lifetime: the Empire takes precedence over any lordship."
Valla's refutation was taken up vehemently by scholars of the Protestant Reformation, such as Ulrich von Hutten and Martin Luther.
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