The Medieval Leap Year and the Red Book of Darley

MS 422, p. 53 (detail)
Christ on a living cross in the Red Book of Darley

The Red Book of Darley is an unusual manuscript- once reputed to perform miracles, it contains both the Old English dialogues of Solomon and Saturn and a liturgical book for what may have been a parish church in Darley Dale in Derbyshire (although was probably at least partially made in Winchester in the 1060s). The text changes between Latin and Old English, with an occasional scattering of runic inscriptions, which are very rare in a manuscript context. A calendar of saints’ days is given in the missal section; the page below is for the month of February, and, a few lines from the bottom, a note is given in Old English regarding the leap year.

MS 422, p. 30

The leap year was a long-established event in Anglo-Saxon England, but in a slightly different form than we currently experience with the Gregorian method of reckoning the year. The Julian calendar, introduced by Julius Caesar in 46 BC (and used until 1752 in England!) removed what was once an entire leap month in the Roman Republican calendar and replaced it with several additional days throughout the year, including one ‘doubled-day’ on the 23rd of February, in which two days were given a single date- VI KL Mar.

The medieval reckoning of days greatly differed from the modern process. Instead of counting forward, simply numbering the days of each month as we do today, a medieval calendar required counting back from the next named day- the kalends, or first of the month; the nones, or nine days before ides, which was the approximate middle of the month (possibly once based on the full moon, then the 13th day for short and the 15th day for long months); and then back to counting back from the next month’s kalends. Thus, calendar tables were required to help sort out what could be an extremely confusing system, as all the subunits of the year needed to fit together in order for the days to even begin to be counted. In the excerpt above from the Red Book, the date is the Roman numeral followed by KL, meaning this portion of the month counts back from the 1st of March.Therefore, calendar creation needed to take the extra day into account in a different way then we do now- instead of having a ‘new date’, there were just two ‘VI KL. Mar.’… in other words, two sixth days before March. The term used for this extra day was ‘bissextum’, or twice-sixth, and a leap year was a ‘bissextile’ year.

The note on the leap year is found starting at v kl, but pertains to the saint’s day on vi kl. It reads, Fif nihton ær februarius beo agan oftúne byð bissextus on Sancte mathias mæssedæg. æfre embe þæt fifte ger.  ðonne freolsa ðu þonne æftran dæg and nim syððan oðerne stæf to sunandæge. It correlates to the problem of the Saint’s day of Matthias, which should occur on VI Kal. Mart, but as that is the bissextum, the confusion lies in whether it falls on the first or second ‘half’ of that doubled-day. The note clears this up by saying that in case of a leap-year, then the feast of St. Matthias would fall on the second half (the 24th in modern parlance). The note also references moving the ‘stæf‘, or letter. This correlates to the column of letters (in black ink in MS 422) that indicates a cycle of weekdays. Each year was assigned a ‘Domenical Letter’ which was the letter on which Sundays would fall, and each date was assigned a letter running A-G, continuously through the year. However, as this note says, in the case of a leap year the Domenical Letter for the year would move back one, in order to maintain the necessary pattern for Easter to fall on the Sunday following the first full moon of after the Vernal Equinox. Confused yet?

This sort of note in a calendar manuscript is not uncommon, but the one in the Red Book is particularly interesting because it is in the vernacular. It demonstrates the creation and use of the manuscript by and for someone who may have been much more comfortable with Old English than Latin. There are numerous instances of this in the manuscript, including an erased note at the top of the February page which translates the Latin text above it. Look for the spidery white letters beneath the red ones:

Calendar erasure

Just to make things slightly more complicated, a lunar month is about 29.5 days long, which runs parallel to the official calendar dating. Because fractions of a day are difficult to keep track o, a medieval calendar split the difference and gave the months ‘full’ or ‘hollow’ labels as they alternated between 29 and 30 lunar days- which did not correspond to solar days. As an example, St. Wulfstan’s Portiforium (MS 391), another 1060s manuscript, also contains a calendar table, but only contains a Latin note on the leap year and the lunar month, which is, in fact, exactly the same wording as the Latin note under the English annotation in the Red Book of Darley (as well as the same as in the Cotton-Corpus Legendary, MS 9, also from the 1060s): Memento quod anno bissextile lune februari xxx dies computes. ut tamen luna martii xxx dies habeat sicut semper. habeat ne paschalis lune ratio vacillet. This reminds the reader that in a leap year, February has an extra lunar day, but March has the same as always (30), so it doesn’t change Easter or April’s lunar positioning.

MS 391, p. 4
Leap year note in St. Wulfstan’s Portiforium

As computational ‘tools,’ manuscript calendars may not always be visually stunning, but, when parsed, often provide valuable information about the location and date of their production, from which we can infer what was important to the people using them and their local community. Keeping track of the years and the variable nature of their constituent parts was a task which kept the procession of holidays and saints’ days in an orderly fashion, in tune with the seasons, and one which required skill and education.

So, this leap day, take a minute to ponder the hundreds of years of complex computations which were required to get to the point in which we can just blithely check our phones for the date without so much as a second thought.





Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Blog at

Up ↑

%d bloggers like this: