Class Handouts:
The Medieval Calendar Updated Jan 2016

The Significator Horarum - The Monastic timekeeper
Modern Time, Medieval Methods. Handout for class and documentation for the winning exhibit for the Stargate Baronial A&S Championship, Stargate Yule, 6 Dec 08.

Coming Someday: I have developed a Shepherd's Dial and a method to design a larger vertical dial both of which show clock time.
Beats pulling out the cell phone from the belt pouch to look at the time! Besides, sundials are more than accurate enough for SCA Standard Time!

Liturgical Calendar

Note: See discussion of Computus Digitorum for explanation of this calendar.
            Liturgical white days are depicted as brown due to limitations of Google Calendar

The Computus Digitorum  
Presenting a Period method of Discerning the Date of Easter, and a Modern Tool to determine the Canonical Hours and Construct a Personal Litrugical Calendar for these Current Middle Ages

The documentation contains the background and explanation and the Excel spreadsheets automate the majority of tasks in building the yearly calendar.

Computus Digitorum Documentation
The following files are Excel spreadsheets, but should also work with OpenOffice and LibreOffice (enable macros!)
Generic Calendar 
Calendar for AD 2008 
Calendar for AD 2009 
Calendar for AD 2010 
Calendar for AD 2011 
Calendar for AD 2012 
Calendar for AD 2013 
Calendar for AD 2014
Calendar for AD 2015
Calendar for AD 2016

This project began in the mid-1990s as an investigation into the Canonical Hours. As with most projects, it didn’t stop there, but expanded to include a general Liturgical Calendar. Next I added the Roman Calendar notation. I had included the table of the Golden Numbers early on, but they were essentially cosmetic, so I had to find out exactly what they had been used for in period. Extrapolating from there, I developed a technique of determining the date of Easter from the Golden Numbers and made them truly functional. The goal then for this calendar is to develop a method of constructing a medieval-style Liturgical calendar for the current modern year that the medievalist can feel a connection to the Middle Ages in form, but maintain modern observances. I believe I have accomplished this by providing a computerized method to remove the tedium of calendar building, but maintaining the flexibility to customize the calendar for personal beliefs and practices. Herein lies the fruits of my research – this documentation of the Medieval Roman Liturgical Calendar in general, and the Excel calendar spreadsheet in specific.

A note on the term Computus Digitorum. I came across this phrase in an abstract discussing the Venerable Bede’s book de temporum ratione (The Reckoning of Time). The computus (Latin: computation) is the technique for calculating the date of Easter, or, more generally, for techniques used in developing a calendar. Bede referred to a method of calculating using his fingers, the computus digitorum. I thought this was an appropriate pun in our modern world of digital computers and thus adopted the name for my computerized calendar.

This document and the computerized version are works in progress. I appreciate comments on how you found it useful or problems you’ve encountered.

The Roman Calendar

The calendar utilized in western Europe during the middle ages was not the universally standardized version we enjoy today. The uniting structure was the major festivals of the Church. Some of these celebrations occurred on fixed dates such as St. John the Baptist or Christmas, while others occurred relative to the movable date of Easter (such as Pentecost).  Dates were commonly referred to by their Church festival rather than the familiar month/day/year used in modern times. It was also quite common to see documents with the dates given in the style used in the ancient Roman empire.

The calendar used in the middle ages in lands that had been in contact with the Romans was developed for Julius Caesar and enacted in 46 BC, and known to us by his name – the Julian Calendar. The Romans set year 1 of their calendar to glorify the founding of Rome in 753 BC. Years counted under this system were referred to as “from the founding of the city,” (AUC). In antiquity the Romans had used year lengths of 10, 11, and 12 months, but by the fall of the Empire the calendar had settled into 12 months with each month having the same number of days as we are familiar with in the 21st century.

Roman Inclusive Counting

Before looking closer at the Roman calendar, there is a quirk of Roman counting that is essential to understanding their system. The Romans used “inclusive” counting which counts both the beginning and ending points, unlike the way we would count in modern times. Using this system, the number of days between dates is one more than the way we would count it. For example, tomorrow would be the second day from now – today=1, tomorrow=2. Have you ever been confused by the Easter story of Jesus being 3 days in the tomb? In modern times we would consider Friday evening to Sunday morning to be a day and a half, or two if you were being generous. However, using the Roman method, you would count Friday as day one, Saturday as day two, and Sunday as the third day. 

Division of the Roman Month 

The month in the Julian calendar was divided into irregular segments, likely to have originally been connected with the phases of the moon. The first day of the month is the Kalends and originally occurred at the new moon. The name comes from the Latin calere – “to call” as the pontifex would “call out” the announcement of the new month as signaled by the sighting of the moon just past new. The next division was the Nones occurring 9 days prior to the Ides and fell on the 5th or 7th of the month. The Ides represented the full moon. The name is derived from iduare – to divide. The Ides is the 15th of the month in March, May, July, and October, and the 13th in January, February, April, June, August, September, November, and December. The remaining days of the month are counted as the number of days before the next Kalends, Nones, or Ides (counting inclusively) and are labeled, e.g. ante diem III Kalends Martius which would be the 28th of February in a leap year. The day before the Kalends, Nones, or Ides is pridie (e.g. Kalends Martius – the last day of February).

Leap Year

A problem that has plagued all calendar systems is there aren’t an even number of lunar months in a solar year. This causes the calendar dates to drift in relation to the seasons. Julius Caesar attempted to fix this drift by adding an extra day to every 4th year to give an average of 365.25 days per year. This was much closer to the actual length of year of 365.2422 days. This slowed the drift of the seasons, but over several centuries it became obvious the dates in the calendar were shifting through the seasons.  

Pope Gregory XIII instituted a more refined system in 1582 that we are still using in our Modern Middle Ages. Leap years occur every 4th year except century years divisible by 400 (e.g., 1600 and 2000). This brings the average days per year to 365.2425 – very close to the actual 365.2422. The actual leap day is inserted after a. d. VI kalendis Martias - 24 Feb) and called bis a. d. VI kalendis Martias and is the origin of the term bissextile to describe a leap year.

The New Year

Even though Dionysius Exiguus defined year one of the calendar when he developed his tables of Easter in the early 6th century, there was still a lot of confusion as to the actual date when the new year started:

"If we suppose a traveler to set out from Venice on 1 March 1245, the first day of the Venetian year, he would find himself in 1244 when he reached Florence: and if after a short stay he went on to Pisa, the year 1246 would already have begun there. Continuing his journey westward, he would find himself again in 1245 when he entered Province, and on arriving in France before Easter (16 April) he would be once more in 1244." Cheney p 8.

The starting points of the calendar that have been used include Christmas, the Annunciation (March 25), Easter, and January first. Christmas Day makes sense since a year numbered based on the birth of Jesus would start on the date celebrated as his birthday. It was used in various locations as late as 14th century. The Annunciation is also called “Lady Day” and was commonly considered the start of the new year in England until the Gregorian calendar was adopted in British lands in 1752. Some areas were one off on the starting year and used dates one year earlier than other locations. Easter Day was used in some parts of France. What goes around, comes around, as January 1 was historically used by the Romans and was recommended for use by both Dionysius and Pope Gregory XIII. It was formally adopted in England with the change to the Gregorian calendar.


The Calendar FAQ

The Ecclesiastical Calendar: It's Theory and Construction by Samuel Butcher published in 1877