<P> The Anglo - Saxon historian the Venerable Bede, who was familiar with the work of Dionysius Exiguus, used Anno Domini dating in his Ecclesiastical History of the English People, completed in 731 . In this same history, he also used another Latin term, ante vero incarnationis dominicae tempus anno sexagesimo ("in fact in the 60th year before the time of the Lord's incarnation"), equivalent to the English "before Christ", to identify years before the first year of this era . Both Dionysius and Bede regarded Anno Domini as beginning at the incarnation of Jesus, but "the distinction between Incarnation and Nativity was not drawn until the late 9th century, when in some places the Incarnation epoch was identified with Christ's conception, i.e., the Annunciation on March 25" (Annunciation style). </P> <P> On the continent of Europe, Anno Domini was introduced as the era of choice of the Carolingian Renaissance by the English cleric and scholar Alcuin in the late eighth century . Its endorsement by Emperor Charlemagne and his successors popularizing the use of the epoch and spreading it throughout the Carolingian Empire ultimately lies at the core of the system's prevalence . According to the Catholic Encyclopedia, popes continued to date documents according to regnal years for some time, but usage of AD gradually became more common in Roman Catholic countries from the 11th to the 14th centuries . In 1422, Portugal became the last Western European country to switch to the system begun by Dionysius . Eastern Orthodox countries only began to adopt AD instead of the Byzantine calendar in 1700 when Russia did so, with others adopting it in the 19th and 20th centuries . </P> <P> Although Anno Domini was in widespread use by the 9th century, the term "Before Christ" (or its equivalent) did not become common until much later . Bede used the expression "anno igitur ante incarnationem Dominicam" (so in the year before the incarnation of the Lord) twice . "Anno an xpi nativitate" (in the year before the birth of Christ) is found in 1474 in a work by a German monk . In 1627, the French Jesuit theologian Denis Pétau (Dionysius Petavius in Latin), with his work De doctrina temporum, popularized the usage ante Christum (Latin for "Before Christ") to mark years prior to AD . </P> <P> When the reckoning from Jesus' incarnation began replacing the previous dating systems in western Europe, various people chose different Christian feast days to begin the year: Christmas, Annunciation, or Easter . Thus, depending on the time and place, the year number changed on different days in the year, which created slightly different styles in chronology: </P>

When did we start using the ad calendar