‘Noon?’ said Sam, trying to calculate. ‘Noon of what day?’
‘The fourteenth day of the New Year,’ said Gandalf; ‘or, if you like, the eighth day of April in Shire reckoning. But in Gondor the New Year will always now begin upon the twenty-fifth of March when Sauron fell (…).’
~ J.R.R. Tolkien: The Lord of the Rings: The Return of the King.
No one any longer celebrates the twenty-fifth of March, and Tolkien’s point is accordingly missed, as I think he intended. He inserted it only as a kind of signature, a personal mark of piety. However, as he knew perfectly well, in old English tradition, 25th March is the date of the Crucifixion, of the first Good Friday. (…) In Gondor, the New Year will always begin on 25th March, and the same is true for England, in a sadly altered fashion. When the Julian Calendar gave way to the Gregorian in 1752, there was an eleven day discrepancy between them, so that the 25th of March jumped to being the 6th of April. And in England the new year still DOES start on the 6th of April. But only the tax year (…).
25th March remains a date deeply embedded in the Christian calendar. In old tradition, again, it is the date of the Annunciation and the conception of Christ – naturally, nine months exactly before Christmas, 25th December. It is also the date of the Fall of Adam and Eve, the FELIX CULPA whose disastrous effects the Annunciation and Crucifixion were to annul or repair. One might note that in the calendar of dates which Tolkien so carefully wrote out in Appendix B, December 25th is the day on which the Fellowship sets out from Rivendell. The main action of THE LORD OF THE RINGS takes place, then, in the mythic space between Christmas, Christ’s birth, and the Crucifixion, Christ’s death.
~ Tom Shippey: J.R.R. Tolkien: Author of the Century
I might add that March 25th forms a sort of bracket around the ‘earthly’ mysteries of the rosary, with the Annunciation being the First of the Joyful Mysteries, and the Crucifixion the last of the Sorrowful Mysteries.
I might also add that March 25th coincides with the time of the Vernal Equinox.