The birth of Mary
As to the place of the birth of Our Blessed Lady, there are three different traditions to be considered.
First, the event has been placed in Bethlehem. This opinion rests on the authority of the following witnesses: it is expressed in a writing entitled "De nativ. S. Mariae" [36] inserted after the works of St. Jerome; it is more or less vaguely supposed by the Pilgrim of Piacenza, erroneously called Antoninus Martyr, who wrote about A.D. 580 [37]; finally the popes Paul II (1471), Julius II (1507), Leo X (1519), Paul III (1535), Pius IV (1565), Sixtus V (1586), and Innocent XII (1698) in their Bulls concerning the Holy House of Loreto say that the Blessed Virgin was born, educated, and greeted by the angel in the Holy House. But these pontiffs hardly wish to decide an historical question; they merely express the opinion of their respective times.
A second tradition placed the birth of Our Blessed Lady in Sephoris, about three miles north of Bethlehem, the Roman Diocaesarea, and the residence of Herod Antipas till late in the life of Our Lord. The antiquity of this opinion may be inferred from the fact that under Constantine a church was erected in Sephoris to commemorate the residence of Joachim and Anna in that place [38]. St. Epiphanius speaks of this sanctuary [39]. But this merely shows that Our Blessed Lady may have lived in Sephoris for a time with her parents, without forcing us to believe that she had been born there.
The third tradition, that Mary was born in Jerusalem, is the most probable one. We have seen that it rests upon the testimony of St. Sophronius, St. John Damascene, and upon the evidence of the recent finds in the Probatica. The Feast of Our Lady's Nativity was not celebrated in Rome till toward the end of the seventh century; but two sermons found among the writings of St. Andrew of Crete (d. 680) suppose the existence of this feat, and lead one to suspect that it was introduced at an earlier date into some other churches [40]. In 799 the 10th canon of the Synod of Salzburg prescribes four feasts in honour of the Mother of God: the Purification, 2 February; the Annunciation, 25 March; the Assumption, 15 August; the Nativity, 8 September.
Taken from
http://www.newadvent.org/cathen/15464b.htm