It is unknown exactly when or why December 25 became associated with Christ's birth. The New Testament does not give a specific date. Tertullian does not mention it as a major feast day in the Church of Roman Africa. In 245, the theologian Origen denounced the idea of celebrating Christ's birthday "as if he were a king pharaoh". He contended that only sinners, not saints, celebrated their birthdays. Sextus Julius Africanus popularized the idea that Christ was born on December 25 in his Chronographiai, a reference book for Christians written in AD 221. This date is nine months after the traditional date of the Incarnation (March 25), now celebrated as the Feast of the Annunciation. March 25 was considered to be the date of the vernal equinox and therefore the creation of Adam; early Christians believed this was also the date Christ was crucified. The Christian idea that Christ was conceived on the same date that he died on the cross is consistent with a Jewish belief that a prophet lived an integral number of years. Thus, the date as a birthdate for Christ is traditional, and is not considered to be his actual date of birth.