Little is known about the origin of the feast, but it can be traced back to the 6th century.
The Bible is silent about the birth of the Virgin Mary, but the Church celebrates it annually on September 8.
This day is universally celebrated in both the East and the West, originally found in the calendars of Eastern Christians.
According to the Catholic Encyclopedia, “The earliest document commemorating this feast comes from the sixth century. St. Romanus, the great ecclesiastical lyrist of the Greek Church, composed for it a hymn … The feast may have originated somewhere in Syria or Palestine in the beginning of the sixth century, when after the Council of Ephesus, under the influence of the ‘Apocrypha,’ the cult of the Mother of God was greatly intensified, especially in Syria.”
The Roman Rite adopted this feast by the 7th century and some claim the date of September 8 came from a particular vision in France.
The church of Angers in France claims that St. Maurilius instituted this feast at Angers in consequence of a revelation about 430. On the night of September 8, a man heard the angels singing in heaven, and on asking the reason, they told him they were rejoicing because the Virgin was born on that night.
However, there is little evidence to support this legend.
On the other hand, there is another tradition that the Virgin Mary was born on a Saturday, according to the 19th-century book The Pilgrim of Our Lady of Martyrs.
According to an ancient tradition she was born on a Sabbath day hence the Sabbath or Saturday has been dedicated by the piety of the faithful to the Blessed Virgin, a devotion which has received the sanction of the Church.
This feast of September 8 was celebrated before the Church honored Mary’s Immaculate Conception on December 8. To calculate that day, the Church simply counted backwards 9 months to arrive at the day of her conception.
Whatever the reality is behind this date, what is true is that the Virgin Mary was born and her birth prepared the way for the coming of Jesus Christ.