The document known to us as the Donation of Constantine is one of the most famous medieval forgeries. Written at an unknown date and place in the heart of the Dark Ages, for unknown purposes, it was embedded in the Forged Decretals in the early 9th century, and so drifted into the main collections of legal material used in the Middle Ages, including Gratian's Decretum. In the absence of a stable political environment in Italy from the collapse of the Roman Empire to the establishment of the modern Italian state, the papacy was obliged to provide for its own security. The document was used to justify it doing so. The text purports to be a legal document issued by the Emperor Constantine, transferring control of Italy and the western provinces to Pope Sylvester in gratitude for being cured of leprosy. The renaissance Popes, whose spiritual role seemed often secondary to their function as the heads of a minor Italian state, used it extensively to oppose the territorial ambitions of the great powers and support their own.
The earliest possible allusion to the Donatio is in a letter in which Pope Hadrian I exhorts Charlemagne to follow Constantine's example and endow the Roman church. It was clearly a defense of papal interests, perhaps against the claims of either the Byzantine Empire or those of Charlemagne himself, who soon assumed the former imperial dignity in the West and with it the title "Emperor of the Romans". The Donation is included among the texts of the False Decretals of Isidore although it is commonly held not to be one of Isidore's own forgeries. Pope Leo IX sent a letter to Michael Cærularius, Patriarch of Constantinople, in 1054, which cited a large portion of the Donation of Constantine believing it genuine. Leo IX assured the Patriarch that the donation was completely genuine, not a fable or old wives tale, so only the apostolic successor to Peter possessed that primacy and was the rightful head of all the Church. The Patriarch rejected the claims of papal primacy, and subsequently the Catholic Church was split in two in the Great East-West Schism of 1054.
However the historical truth is that the Church only officially acquired the papal lands in 756 A.D. when King Pepin of the Frankish Empire gave them to the Church as a gift. 756 A.D. also appears to be the time when the text of the Donation first appeared. It was probably created by a cleric either in Rome or the Frankish court. Its purpose may have been to allow the King to claim that he was returning, not giving, the papal lands to the Church. In this way, the fiction of the Donation added legitimacy to a convenient political marriage between the Catholic Church and the Frankish state.
But in the Renaissance, for the first time in a millennium, it was possible to compare such documents with the genuine products of antiquity. St. Nicholas of Cusa was one of the first to notice that the Donation did not agree with the picture given by other documents. But it was left to the quarrelsome but brilliant scholar Lorenzo Valla to make public that the document was a fraud. This he did around 1450, while working for King Alfonso of Aragon, Sicily and Naples, who was attempting to make claims to various parts of Italy.
Lorenzo Valla enumerated the large number of historical anachronisms that pervaded the work. For instance, it referred to Byzantia as a province when in the fourth century it was only a city, it referred to temples in Rome that did not yet exist, and it referred to 'Judea' even though in Constantine's time the Romans referred to this territory as 'Palestina.' Valla could have added that Emperor Constantine never had leprosy, making it impossible for Pope Sylvester to have cured him of this disease. The Catholic Church suppressed Valla's work for years. Centuries later, it publicly conceded that the Donation was a fake.
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