The article reexamines the origins of the legend of the donation which Emperor Constantine the Great was to make to Pope Sylvester I, offering him Rome and the secular power over the western part of the Roman Empire. Its main purpose is to analyze how the hagiographical text produced in the late fifth century to promote the cult of St. Sylvester was adopted and used by medieval popes to endorse their dominant position in Latin Christendom. The charter of Constantine’s Donation became one of the most famous medieval forgeries, which served to legitimize the existence of papal state in Italy and to promote the idea of popes’ superiority over emperors and other secular rulers. It was only in the middle of the fifteenth century that the authenticity of that document was successfully questioned by Nicholas of Cusa and in particular by Lorenzo Valla. The latter in his treatise De falso credita et ementita Constantini Donatione by means of a careful historical and philological analysis demonstrated that Constantine’s Donation was a pure forgery. and Paweł Kras.