The medieval calendar served a number of purposes, one of them being to keep track of the date and another to know which days were feast days of the Church – holidays. Dates were not computed in the manner we are now accustomed to. Every month had three reference days, and all the other days were named according to how many days off the next reference day they were.
Medieval date numbering was rooted in ancient Rome and was based on three reference days per month: Kalendae, Nonae and Idus. Kalendae always came on the first day of the month (hence the name calendarium, calendar), Nonae came on the fifth day of every month except March, May, July and October, when they came on the seventh day, and Idus came on the 13th of every month except March, May, July and October, when they came on the 15th. The other days of the month were numbered off backwards in time from the nearest reference day.
After Kalendae, the first day of the month, you proceeded to count backwards from Nonae, so that the 2nd of the month would be called four (or six, depending on which month) days before Nonae (IV ante nonas), the 3rd three days before Nonae (III ante nonas) and so on. After Nonae the count-down continued until Idus and thereafter until Kalendae. The last day of the month was described as two days or one day before Kalendae (II ante Kalendas or Pridie Kalendas).
In the calendarium, the Roman numerals counting down to the next reference day are shown in a column to the left of the abbreviations of the reference days, with KL or K standing for Kalendae, N for Nonae, and ID for Idus. Each new monthly page starts with a large KL, often decorated. Sometimes too the pages are embellished with miniatures of the zodiac.
The third column gives different feast days observed by the Catholic Church during the month concerned. Because the medieval calendar was meant to remain serviceable for an indefinite number of years – a “perpetual” calendar – the feast days shown were those with fixed dates. Feasts celebrated on different dates in different years – such as Easter or Paschal holidays – were not included. Feast days comprised a number of saints’ days and certain “red-letter” days of the Church’s year, such as Christmas and Epiphany(Lat. Nativitas domini) [311r], Lat. Epiphania) [305v].
The canon of saints varied according to the origin and age of the calendar. Saints were added or faded away with the passing years. The ever-present core consisted of the universal saints’ days of the Church. These included feasts of the Virgin Mary, commemorating important events in her life, such as her birth, purification and annunciation (Nativitas Mariae 8th September, [309v] Purificatio Mariae 2nd February [306r] and Annuntiatio Mariae 25th March. [311r])
The death days of the apostles, evangelists and martyrs were also universal feast days. They included, for example, the feast of Ss Peter and Paul on 29th June, that of John the Baptist on 24th June [308r] and St Lawrence on 10th August [309r]. The death days of the saints were counted by the Church as their true, i.e. heavenly, birthdays.
The cult of saints from the missionary period and of saints introduced by the Benedictine Order – which was highly influential in early medieval times – was almost as widespread as the earliest universal saints’ days. For example, the cult of St Boniface, the apostle of the Germans, 5th June [308r], and that of Benedict, founder of the Benedictine Order, 21st March [306v], encompassed several provinces of the Church. Saints whose popularity soared during the crusades, such as Nicholas of Myra, 6th Dec. [311r], and the saints of the later religious orders, also eventually acquired very strong standing everywhere in the Catholic Church.
The cult of local saints could be confined to a province of the Church, a bishopric, a parish or, in rare instances, a single church. Often it centred round the possession of relics of the saint. The geographic limitation of the cult of these saints makes them very interesting. Erik and Bridget (Birgitta), for example, are numbered among Sweden’s local saints. The Devil’s Bible features several Bohemian local saints. Vaclav (Lat. Wenceslaus), the Bohemian duke martyred in 935, is inscribed in the manuscript’s calendarium in three different places: on his death date, 28th September [309v], on 5th October [310r], the octave of his feast day (i.e. eight days after it), and on 4th March [306v], which is the date of his translation, meaning the transfer of his relics to Prague, probably in 938. All this bears witness to the outstanding importance of the cult of Vaclav in Bohemia at the time of the Devil’s Bible’s compilation. Moreover, all three festivals are inscribed in red ink, denoting their superlative degree.
Medieval calendars had a special way of indicating a saint’s importance. Most saints’ names were written in black or brown ink, but the names of the most important ones were entered in red, sometimes blue or green ink, and sometimes even lettered in gold.
Information regarding the degree of the feast could be made still more precise, especially in liturgical books, by means of such designations as duplex (double), simplex (single), semiduplex (a festive degree in between duplex and simplex) and an indication of the length of lessons during the daily prayers before dawn.
The occurrence of a particular saint in the calendar can facilitate the dating of a manuscript. Such is the case, for example, with St Procopius, founder and abbot of the Bohemian monastery of Sazava, who died in 1053. His name is inscribed in the Codex Gigas on 4th July [308v]. Given that he was canonised in 1204, this makes him the most recent saint in the entire Codex Gigas, which in principle tells us that the manuscript could not have been written before that year.
To the left of the reference day designations is a column of “golden numbers” and another containing a series of letters of the alphabet, from A to G, known as dominical letters and repeated a number of times. Both were needed for computing the date of Easter for the year concerned. In 325 AD it had been decreed that Easter was to come on the first Sunday following the first full moon after the vernal equinox.
The golden numbers go from I to XIX, though not in sequence, and with gaps in between, and they show the date of the new moon for each month. The seven dominical letters stand for the days of the week, with each letter corresponding to one day of the week throughout the year. Both golden numbers and dominical letters were computed annually by a special system.
The calendar also shows the number of calendar days and the estimated duration of the lunar cycle from one new moon to the next, expressed in a full number of days. In Codex Gigas they are inscribed at the top of each monthly page.
The actual calendar text also includes a number and variety of notices, e.g. concerning the initial days of the seasons (veris initium, 7th February, the beginning of spring, the date of the sun’s entry into signs of the zodiac (sol in pisces, 16th February, the sun’s entry into Pisces) [f.306r] or the indication of firm dates of biblical events, such as the creation of the world (Primus dies seculi, 17th March)[f.306v]. Notes recording major events could also be added to the calendar.
In addition the Codex Gigas contains a number of necrologies. These mainly comprise the names of deceased members of the monastic community, benefactors of the monastery and certain historically important personages to be commemorated by the monastery on their death days.
The medieval calendar was a supremely organic corpus: new saints were added to it, sometimes saints were deleted, notes were entered and one and the same calendar remained in use, not just for years but sometimes for centuries. Surprisingly, therefore, the Codex Gigas contains hardly any additions in a different hand from the rest of the manuscript.