How Did the Church Determine That September 8 Is the Birthday of Our Blessed Mother?

Usually, the Church assigns dates for particular feasts. The assignments can be based on the date of a saint’s death, a date that has special meaning in the saint’s life, or some other meaningful date. In the case of the Nativity of the Blessed Mother, September 8 is the date that follows nine months after December 8, on which date the Church celebrates the feast of the Immaculate Conception of Mary.