 Latin Rite Catholics considered it inappropriate that Constantine was baptized only on his death @-@ bed and by an unorthodox bishop , as it undermined the authority of the Papacy . Hence , by the early fourth century , a legend had emerged that Pope Sylvester I ( 314 – 335 ) had cured the pagan emperor from leprosy . According to this legend , Constantine was soon baptized , and began the construction of a church in the Lateran Palace . In the eighth century , most likely during the pontificate of Stephen II ( 752 – 757 ) , a document called the Donation of Constantine first appeared , in which the freshly converted Constantine hands the temporal rule over " the city of Rome and all the provinces , districts , and cities of Italy and the Western regions " to Sylvester and his successors . In the High Middle Ages , this document was used and accepted as the basis for the Pope 's temporal power , though it was denounced as a forgery by Emperor Otto III and lamented as the root of papal worldliness by the poet Dante Alighieri . The 15th century philologist Lorenzo Valla proved the document was indeed a forgery . 
