Given the importance of calculating when significant religious occasions should be observed, he formulated a new table of when the holiday would fall, starting from a year he called “532.” He wrote that this method of counting “with years from the incarnation of our Lord Jesus Christ” would replace a system based on the Roman Emperor Diocletian’s rule which he termed “the memory of an impious persecutor of Christians.” But just because he used this dating didn’t mean it was popular or caught on immediately, or that he was necessarily the first to or only one to do so. One of the early writers to date this way was Dionysius Exiguus, a monk who, in 525 A.D., was intent on working out when exactly Easter would occur in the coming years. In Christian Europe Jesus is the obvious point of departure,” explains Hunt. “Christians wanted to get away from the Roman chronology, so they begin to develop a Christian chronology. Get your history fix in one place: sign up for the weekly TIME History newsletter