The O Antiphons (also known as the Great Advent Antiphons or Great Os) are Magnificat antiphons used at vespers on the last seven days of Advent in Western Christian traditions. They likely date to sixth-century Italy, when Boethius refers to the text in The Consolation of Philosophy. They subsequently became one of the key musical features of the days leading up to Christmas.
Although the antiphons and dates shown above have been fairly universally recognised throughout western Christendom, an alternative English medieval practice arose of moving all of the antiphons forwards by one day (commencing therefore on 16 December) and adding another (eighth) antiphon on 23 December, with the acrostic thus becoming Vero cras, "truly, tomorrow". This is the antiphon O Virgo virginum (O Virgin of virgins), with the following text:
O Virgo virginum, quomodo fiet istud?
Quia nec primam similem visa es nec habere sequentem.
Filiae Jerusalem, quid me admiramini?
Divinum est mysterium hoc quod cernitis.
O Virgin of virgins, how shall this be?
For neither before thee was any like thee, nor shall there be after.
Daughters of Jerusalem, why marvel ye at me?
The thing which ye behold is a divine mystery.
Given the English origins of this alternative, it has traditionally been the version used in the Church of England (including Canterbury Cathedral) until recent times, and is the version printed in traditional Church of England liturgical sources including the English Hymnal and New English Hymnal. From 2000, however, the Church of England appears to have taken an official step away from English medieval practice towards the more widely spread custom, as Common Worship makes provision for the sevenfold version of the antiphons, and not the eightfold version.