The Donation of Constantine (Constitutum Constantini), written probably not long after the middle of the eighth century, became widely known through its incorporation in the Pseudo-Isidorian Decretals (about 847-853). Parts of it were included in most of the medieval collections of canon law; Anselm’s, Deusdedit’s, and Gratian’s great work (the Decretum, or Concordia discordantium canonum). It purports to reproduce a legal document in which the Emperor Constantine the Great, reciting his baptism and the cure of his leprosy at the hands of Sylvester, Bishop of Rome 314-336, confirmed the privilege of that pontiff as head of all the clergy and supreme over the other four patriarchates; conferred upon him extensive imperial property in various parts of the world, especially the imperial Lateran palace, and the imperial diadem and tiara, and other imperial insignia; granted the Roman clergy the rank of the highest Roman orders and their privileges; gave Sylvester and his successors freedom in consecrating men for certain orders of the clergy; it tells how he, Constantine, recognized the superior dignity of the Pope by holding the bridle of his horse; grants Sylvester Rome, all of Italy, and the western provinces, to remain forever under the control of the Roman See; and states his own determination to retire to Byzantium in order that the presence of an earthly emperor may not embarrass ecclesiastical authority. This remarkable document was almost universally accepted as genuine from the ninth to the fifteenth century. The question of the position of the bishop of Rome in the Christian Church lacks but a few generations of being as old as Christianity itself. His relation to secular governments became an acute problem as soon as the imperial government broke down in Italy, and has remained so to the present moment. For centuries the Papacy was the strongest institution in western Europe. While its control at any one time rested principally on the power it actually possessed and on the ability of its representatives, legal theories and historical documents played a not inconsiderable part in its rise and decline. Of these documents the Donation of Constantine was perhaps the most spectacular, even though it was not the most important. It was cited by no less than ten Popes of whom we know, to mention no lesser writers, in contentions for the recognition of papal control, and contributed not a little to the prestige of the Papacy. On the other hand, when its spuriousness became known, the reaction against it, as in Luther’s case, contributed powerfully to the revolt from Rome. Its century-long influence entitles it to a respect difficult for any one who now reads it to feel. And Valla’s discussion of it contains many interesting reflections on the secular power of the Papacy, perhaps the most interesting expression in this connection of fifteenth century Italian humanism.