For the first six centuries since the birth of Jesus Christ, European countries used various local systems to count years, most usually regnal years, modelled on the Old Testament. In some cases, Creation dating was also used. In the 6th century, the Christian monk Dionysius Exiguus devised the Anno Domini system, dating from the Incarnation of Jesus. In the 8th century, the Anglo-Saxon historian Bede the Venerable used another Latin term, "ante uero incarnationis dominicae tempus" ("the time before the Lord's true incarnation", equivalent to the English "before Christ"), to identify years before the first year of this era.
According to the Catholic Encyclopedia, even Popes continued to date documents according to regnal years, and usage of AD only gradually became common in Europe from the 11th to the 14th centuries. In 1422, Portugal became the last Western European country to adopt the Anno Domini system.
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