The Church has celebrated Mary’s birth since at least the sixth century. A September birth was chosen because the Eastern Church begins its Church year with September. The September 8 date helped determine the date for the feast of the Immaculate Conception on December 8.
Scripture does not give an account of Mary’s birth. However, the apocryphal Protoevangelium of James fills in the gap. This work has no historical value, but it does reflect the development of Christian piety. According to this account, Anna and Joachim are infertile but pray for a child. They receive the promise of a child who will advance God’s plan of salvation for the world. Such a story, like many biblical counterparts, stresses the special presence of God in Mary’s life from the beginning.