If you were an Englishman or Irishman of the past with quarterly rents to pay, you'd better know what today was. March 25 marks the Feast of the Annunciation of the Blessed Virgin Mary in the Roman Catholic Church, but it's also an old British Quarter Day, commonly known as Lady Day.
From at least the 12th c. to the mid-18th c., Lady Day was the beginning of the new business year. Lady Day was the day when annual contracts between landowners and landlords and their tenants would be renewed, rents fell due, and servants were hired.
Despite its Christian name (the "Lady" honors the Virgin Mary), the day's roots are more agricultural than religious. March 25 is the equinox, the day when day and night are the same length. To ancient pagans more in tune with nature's cycles, this seemed to be a fit place to begin the new year, and much more convenient than in the middle of snowy winter. It was also a good day for farmers to take time to tend to business matters, falling as it does neatly between plowing and harvest.
When England switched from the Julian to the Gregorian calendars in 1752, the first of January became the official beginning of the new year, and Lady Day lost much of its significance. It does, however, linger in the minds of modern English taxpayers. April 6, or Old Lady Day (adjusted with the days that were "lost" by the calendar change) is the English Tax Day.
Above: The Annunciation, by Sandro Botticelli, c. 1490, Uffizi Gallery, Florence