A mysterious birth…
Although this date is listed in the Christian liturgical calendar as that of the birth of Mary, there is no biblical text confirming it. The New Testament does not mention the place, date or circumstances of his birth.
… but miraculous
A detail about Marie’s parents is however mentioned in the Protevangele of James. It is an apocryphal gospel: a story that does not appear in the Bible and whose authenticity is not verified. However, we learn there that Marie would be the daughter of Anne and Joachim whose birth of the child would be a miracle. According to the text, Anne is sterile and her husband, afflicted, withdraws into the desert to implore heaven to give him descendants. While everything seems in vain, an angel introduces himself to Anne, then to Joachim and announces to them that they will soon give birth to a child.
Why September 8?
According to Eastern tradition, a church would have been erected near the house of Anne and Joachim in Jerusalem: the Church of Saint Anne, consecrated on September 8. In the 7th century, Pope Sergius I fixed this date as that of the birth of Mary and registered it as a Marian feast with that of the Immaculate Conception (celebrated on December 8).