The article is dedicated to the study of disputes over the specification of the date of the celebration of Easter during the pontificate of Leo the Great (440-461). Two times during his pontificate, in 444 and in 455, due to the discrepancy between the Roman and Alexandrian Paschalias, Leo was forced to discuss the exact date of the celebration of Easter with the Church of Alexandria. The article, on the basis of the evidence contained in the letters of Pope Leo and his correspondents, analyzes the reasons why in both these cases the pope was forced to cede authority to the Alexandrian tradition. In addition, the context of inter-church and church-state relations, against which these disputes took place, is analyzed, and their stages are clarified. The paper analyzes the letter of Proterius of Alexandria that contained explanations about the Alexandrian Paschalia, and also analyzes in detail the content of the paschalistic treatise by Victorius of Aquitaine, in which the latter attempted to reconcile the Roman and Alexandria method of calculating the date of Easter. The authors suppose and give reasons for the supposition that Victorius began working on his treatise in 454 after receiving a letter from the Roman archdeacon Hilarus, drawn up between January and April of the same year. Basing on the analysis of the role of the Emperor Marcian (450-457) in this dispute, the authors conclude that in fact Pope Leo was obliged to obey to the decision of the emperor concerning church life.
