Dominical Letter - History

History

Dominical letters were a device adopted from the Romans by chronologers to aid them in finding the day of the week corresponding to any given date, and indirectly to facilitate the adjustment of the "Proprium de Tempore" to the "Proprium Sanctorum" when constructing the ecclesiastical calendar for any year. The Christian Church, due to its complicated system of movable and immovable feasts, has long been concerned with the regulation and measurement of time. To secure uniformity in the observance of feasts and fasts, it began, even in the patristic age, to supply a system of reckoning (computus) by which the relation of the solar and lunar years might be accommodated and the celebration of Easter determined. It adopted the astronomical methods that were available at the time, and these methods and their methodology have become traditional and are perpetuated in a measure to this day, even the reform of the calendar, in the prolegomena to the Breviary and Missal.

The Romans were accustomed to dividing the year into nundinæ, periods of eight days; and in their marble calendars (fasti), of which numerous specimens remain, they used the first eight letters of the alphabet (A to H) to mark the days of which each period was composed. When the Oriental seven-day period (week) was introduced in the time of Cæsar Augustus, the first seven letters of the alphabet were employed in the same way to indicate the days of the new division of time. Some surviving (albeit fragmentary) marble calendars show both cycles side by side (see "Corpus Inscriptionum Latinarum", 2nd ed., I, 220; the same peculiarity occurs in the Philocalian Calendar of A.D. 356, ibid., p. 256). This device was imitated by the Christians.