Mary’s Birthday

Today is the Nativity of Mary, a Roman Catholic feast day celebrated exactly nine months after the Feast of the Immaculate Conception. It’s celebrated in Catholic schools, which in the Philippines means the majority of private schools. Being a non-biblical doctrine, I can’t figure out how this date was chosen. Did it supplant an earlier pagan holiday, as some other Christian holidays were?

Update: I found this from the Catholic Encyclopedia:

Since the story of Mary's Nativity is known only from apocryphal sources, the Latin Church was slow in accepting this oriental festival. It does not appear in many calendars which contain the Assumption, e.g. the Gotho-Gallican, that of Luxeuil, the Toledan Calendar of the tenth century, and the Mozarabic Calendar. 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 8 Sept., 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 (La fête angevine N.D. de France, IV, Paris, 1864, 188); but this tradition is not substantiated by historical proofs. The feast is found in the calendar of Sonnatius, Bishop of Reims, 614-31 (Kellner, Heortology, 21). Still it cannot be said to have been generally celebrated in the eighth and ninth centuries. St. Fulbert, Bishop of Chartres (d. 1028), speaks of it as of recent institution (P.L., cxli, 320, sqq.); the three sermons he wrote are the oldest genuine Latin sermons for this festival (Kellner, "Heortology", London, 1908, 230). The octave was instituted by Innocent IV (a. 1243) in accordance with a vow made by the cardinals in the conclave of the autumn of 1241, when they were kept prisoners by Frederick II for three months.

So, the September 8 date for the birth of Mary did not come from a pagan original but from visions of an unnamed mystic (it is the Roman Catholic Church after all). The apocryphal source alluded to in the above excerpt probably refers to the Infancy Gospel of James, which discusses the Nativity of Mary but does not give an exact date.