Of course, Dionysius was careful to couch his work in terms that would be acceptable to the spiritualists of his day, insisting in explanations about his work that the holy day of Easter should be calculated ‘not so much from worldly knowledge, as from an inspiration through the Holy Spirit’. He then promptly turned to astronomy and mathematics to make his calculations, adopting what in those days was the most accurate method available, the 19-year lunar cycle. Essentially he updated the table computed by the Alexandrian bishop Cyril, extending it for another 95 years, from 532 to 627.
Year (AD)
532
533
534
535
Indiction (I)
10
11
12
13
Moon’s Phase (II)
0
11
22
3
Day of the Week of March 24 (III)
4
5
6
7
Year in 19-Year Lunar Cycle (IV)
17
18
19
1
First Day of Passover (V)
Nones April
8 Kalends April
Ides April
4 Nones April
Easter Sunday (VI)
3 Ides April
6 Kalends April
16 Kalends May
6 Ides April
(11 April)
(26 March)
(16 April)
(8 April)
We needn’t plunge too deeply into the numeric complexities of these long-forgotten tables, although a brief dip will help explain what a man such as Dionysius knew and had to work with as he struggled to make sense of his Christian-Roman calendar. For example, in the chart below are four years in Dionysius’s first 19-year cycle:*
*He is using the old Roman system of kalends, ides and nones, which would linger throughout the Middle Ages.
Below are explanations of each of the lines headed up by a Roman numeral:
I: This number has nothing to do with calculating Easter. It refers to a system of dating Roman documents in 15-year cycles called indictions, a style of dating so widely used for financial and legal documents (often in conjunction with the date of a consul or emperor’s reign) that Dionysius included it as a helpful guide to the year for those using his table.
II: To calculate the true Easter, astronomers started by noting the ‘age’--or phase--of the moon during a given year on a set date in the solar calendar. This was arbitrarily set by Dionysius at 22 March, the day after the official spring equinox as determined at the time of the Council of Nicaea. For instance, in 532 the moon’s age was o days old on 22 March--a new moon. This age-number is called an epact. Because the lunar years runs 11 days fast against the solar year, the age of the moon on any given date in the Julian calendar will always be 11 days ‘older’ the next year. Thus in 533 the epact of the moon was not 0, but 11.
A year later, in 534, the epact moved another 11 days back, for a total of 22 days of movement since 532. But because the moon runs in a 295 day cycle (rounded up to 30 days by Dionysius), the next year, 535, has an epact of 3, determined by taking 22+11 + 33--the 30-day month + 3. And on it goes with eleven added to each year, running on a 30-day cycle.
The epact is important because in the 19-year lunar cycle this number will always be the same for each year in the cycle. (See number of the year in the 19-year progression.) This formula made it simple for anyone with even a rudimentary knowledge of numbers to calculate Easter, though later time reckoners would realize that the moon does not fit precisely into this cycle, since the lunar month is actually less than 30 days. Whether or not to use epacts became a hotly debated topic during the deliberations in the sixteenth century that led to the Gregorian reforms in 1582.
Ill: This is the day of week that fell on 24 March, which was used to determine on which date the Sunday after the equinox would fall.
IV: The year in the 19-year lunar cycle.
V: This is the beginning of Passover, corresponding to 14 Nisan in the Jewish calendar--a date that Christian time reckoners were ordered to avoid by the bishops at Nicaea, who dictated that Easter could never be held on the day Passover begins. If the calculations for Easter indicate a date on 14 Nisan, the celebration was moved to the following Sunday.
VI: The correct date each year for Easter Sunday, based on the formula in use at the time of the Council of Nicaea in 325. This has Easter falling on the first Sunday after the first full moon after the spring equinox.
Dionysius, like other Easter time reckoners past and present, provides numerous equations that prove the interconnectedness of these dates mathematically.* These are practical for the serious ecclesiastic task at hand but also seem in their elegance to be the product of a mind that enjoyed the precision and exactitude of equations for their own sake, despite his devout talk about ‘the Christian concept of time’.
*One flaw in Dionysius’s system was the impossibility of matching up the seven-day week, in which Sunday fell, mathematically with a 95-year period of 19-year cycles. Obviously seven does not divide into 95, which meant this table was still not entirely accurate as a predicdve tool. A mathematician in Aquitaine named Victorius figured out a solution to this problem c. 457 by figuring out that Easter dates repeat themselves every 532 years, 532 being a number divisible by 19 and by 7. Apparently Dionysius was unaware of Victorius’s discovery.
Dionysius’s contribution to our calendar went far beyond the pedestrian task of calculating another 95 years of Easters. When he published his tables he included a reform that was little noticed in his own day but now affects virtually everyone in the world: the system of dating known as anno Domini (AD), ‘the year of our Lord’--which many people now call the common era (CE).
In a letter to a bishop named Petronius, Dionysius complained that earlier Easter tables used a calendar widely followed at the time, which started its year one in AD 284, the year that Emperor Diocletian ascended to the throne. Under this system, the year Dionysius wrote his letter--which we call AD 531--was designated the year 247 anno Diocletiani, the year of Diocletian. But Diocletian was a notorious persecutor of Christians, noted Dionysius, who tells Petronius that he ‘preferred to count and denote the years from the incarnation of our Lord, in order to make the foundation of our hope better known and the cause of the redemption of man more conspicuous.’ Dionysius calculated that Christ was born exactly 531 years earlier--which became his base year of AD 1. (Dionysius did not designate a year 0 because the concept of zero had not yet been invented.) Where the abbot got this date for Christ’s birth is unknown. Nor is it clear if his scheme was an original idea or one already informally used. Whatever the source, Dionysius was the first ever to use the system we all now take for granted when he wrote on his Easter tables anni Domini nostri Jesu Christi (the years of our Lord Jesus Christ) 532-627.
Unfortunately, Dionysius almost certainly got his dates wrong. The true moment of Christ’s birth is unknown and a matter of immense controversy even today, given the vague and contradictory information available on Christ’s early life. The Gospel of Matthew claims he was born in the time of Herod the Great, who died in 4 BC. This means the birth must have occurred before this date. Other Gospels and historical sources suggest dates ranging from 6 or 7 BC to AD 7, though most historians lean toward 4 or 5 BC. This means the year 1996 or 1997 was probably the true year 2000 in the anno Domini calendar, if one does the arithmetic without a year 0.
Anyway, it took time for Dionysius’s use of anno Domini to catch on. Some Christians resisted it because they preferred the anni Diocletiani, also called the ‘Era of the Martyrs’, a period held in veneration despite its association with an anti-Christian emperor. (Coptic Christians in Egypt still use anni Diocletiani; for them, the year AD 2000 will correspond to the year 1716 in the ‘Era of the Martyrs’.) It was Dionysius’s friend Cassiodorus who first used the AD system in
a published work when he and his monks wrote their textbook in 562 on how to determine Easter and other dates, the Computus paschalis. Other Italians gradually accepted the AD system over the next several decades, followed very slowly by other regions of Christendom.
Early Catholic missionaries introduced the system in Britain, where newly converted Saxons issued edicts dated with anno Domini in the seventh century. It first appeared in Gaul during the eighth century but did not come into wide use in Europe until the tenth century. In some outlying provinces, including parts of Spain, the AD system was not adopted until the 1300s. Christians did not use the inverse of anno Domini, BC (for ‘before Christ’) until 1627, when the French astronomer Denis Petau apparently became the first ever to add BC to dates while teaching at the College de Clermont in Paris.
Soon after the elderly Cassiodorus published his textbook on computus in 562 the eastern emperor Justinian died, leaving his ambition to re-establish the Western empire unrealized. His efforts ultimately proved disastrous to the West, as he and his immediate successors found themselves overextended and unable to fend off fresh assaults by Lombards, Bavarians, Saxons and other Germanic tribes. Even worse, these previously obscure invaders were far less Romanized than the Germans Justinian had destroyed, barbari who had long associated with Rome on the border of the old empire. With homelands deep in the hinterlands of Europe, the newcomers were far more rapacious and thorough in their ravaging and in establishing tribal-style governments. The Byzantines retained a toehold in Ravenna and in other parts of Italy for several more decades, and remained a presence for centuries to come. But in the wake of Justinian’s juggernaut, most of the West collapsed again into near anarchy, with the only remnant of central authority residing in the Church.
Boethius’s execution in 524 had signalled the instability of an age that had little interest in intellectual pursuits. But the death of Cassiodorus sometime in the 580s--presumably safe behind his monastic walls--symbolized the final gasp of an ordered world where time had mattered and calendars framed how most people lived, worked and worshipped. With the West now a political and intellectual wasteland, people had little need for formal civil calendars, with most reverting back to a preliterate age when farmers, sailors and merchants measured time as the Greeks did in Hesiod’s days--in broad cycles where events were triggered by the bloom of a flower or the flight north or south of flocks of birds. For much of Rome’s illiterate population this had always been the way time was measured. But now, as Boethius lamented in his Consolation, the entire culture seemed to be sliding into an abyss:
For who gives in and turns his eye
Back to the darkness from the sky,
Loses while he looks below
All that up with him may go.
Time had finally come to a full stop. Or at least it seemed this way, though remarkably a few monks and scholars over the coming centuries would keep the mechanism of calendar time moving, if barely. Indeed, the story of the calendar now shifts to one of the greatest of these medieval lights, a man who lived not in Rome or some other ancient centre of culture, but on a shadowy island on the edge of what was to these Europeans the known world.
6 Monks Dream While Counting on Their Fingers
It is said that the confusion in those days was such that Easter was sometimes kept twice in one year.
Bede, AD 731
Under an ancient gnarled oak tree in south-west England the first Archbishop of Canterbury held a meeting sometime in the late 590s--about a decade after Cassiodorus died in Italy--to settle a local dispute over Easter.
The archbishop, a Greek named Augustine,* was trying to convince a delegation of Celts from the western side of the island to abandon their system of calculating the Easter date, which deviated from St Peter’s. Isolated since the last imperial legion abandoned the island in 410, these Celts had been Christianized late in the Roman era only to find themselves cut loose soon after from both the empire and the Church in Rome. Since then waves of invasion by Saxons and Angles had driven these ancient Britons into what is now Wales, where they had joined with other Christian Celts from Ireland to form an independent church, with its own ideas about dating the Resurrection.
*This is not Augustine of Hippo
Augustine, dispatched to Britain by the pope to evangelize the Saxons and to Romanize the Celts, insisted that God was on his side. To prove it he reportedly performed a miracle under that old oak tree--restoring sight to a blind man.
The Celts were impressed but unconvinced. ‘Whereupon Augustine ... is said to have answered with a threat that was also a prophecy,’ writes the British monk Bede (672-735), recounting the story a century later, ‘telling the Britons that their intransigence would one day cause their destruction.’
Sure enough, wrote Bede, a few years later a brutal Saxon king named Aethelfrith (d. 616) ‘raised a great army and made a great slaughter of the faithless Britons.’ The dead included 1200 unarmed monks massacred near their monastery at Bangor. That King Aethelfrith was a butcher intent on expanding his tiny kingdom at the expense of Celts; and that he was a pagan who cared nothing about Easter, hardly mattered to Bede and other Christians siding with Rome in this murky, little-known corner of Europe. For them the massacre was the fulfilment of Augustine’s prophecy against these ‘faithless Britons, who had rejected the offer of eternal salvation, would incur the punishment of temporal destruction’.
And what was the difference between the two churches’ dates for Easter?
A single day.
You see, the Celts placed the date of Christ’s crucifixion on a Thursday instead of a Friday. This meant their Easter had to fall (according to the Jewish calendar) between 14 and 20 Nisan, while Rome said the date must fall between 15 and 21 Nisan--a difference so minor that it is hard to imagine anyone quibbling to the point of bloodshed. Especially given the fact that Bede himself, one of the most brilliant time reckoners in the Middle Ages, knew something that almost no one else did in this murky era: that Rome’s official dating of Easter was itself in error, because the Julian calendar it was based on was flawed.
Bede was almost sixty years old in 731 when he published his account of the prophecy and slaughter in his Ecclesiastical History of the English People. A monk, teacher and choirmaster at the Saxon-era monasteries of Wearmouth and Jarrow in Northumbria, he lived far away from the centres of culture and learning (such as they were) in his age--which makes his accomplishments all the more astonishing. For without ever leaving the neighbourhood of his twin monasteries, Bede wrote some sixty books on subjects ranging from commentaries on the Bible to works on geography, history, mathematics and the calendar. He penned detailed letters describing the concept of the leap year, his calculations about the supposed motion of the sun around the earth, and his measurements of equinoxes. He even came up with the name calculator to describe a time reckoner, and later catholicus calculator--’Catholic calculator’.
‘I was born on the lands of this monastery,’ Bede wrote in his History. ‘I have spent all the remainder of my life in this monastery and devoted myself entirely to the study of Scriptures. And while I have observed the regular discipline and sung the choir offices daily in church, my chief delight has always been in study, teaching and writing.’ Handed over to the abbot of the monastery by his apparently upper-class family at the age of 7, he was educated by the monks, became a church deacon at 19, and was ordained a priest at 30--all at Wearmouth and Jarrow.
Built in the latter part of the seventh century, Wearmouth was founded shortly after Bede’s birth in 672 on the coast of England near where the River Wear pours into the North Sea--a country of rolling hills, limestone and sandstone outcrops, low mountains, and ruined Roman walls and towns. The monks built a companion monastery nine or ten years later at Jarrow, a few miles away on the mudflats at the confluence of the Don and Tyne Rivers. Both began as Saxon structures of timber and straw until one of the project’s sponsors, a monk of noble birth named Benedict Biscop (c. 628-690
), decided the buildings should look like the stone churches he had seen during his travels in Gaul. With Hadrian’s ruined wall and an old Roman fort nearby, stone was readily available for pilfering, though Benedict Biscop had to bring over skilled labour from Gaul because Britain lacked master builders and stone masons. He also brought across the channel glassmakers who glazed the windows and made glass receptacles.
Benedict filled his buildings with a rich assortment of imported altar vessels, paintings and carvings--and with a library. Taking five trips to Rome, Benedict brought back ‘a great mass of . . . books’, including calendars--among them almost certainly Dionysius Exiguus’s charts and calculations, and the latest martyrologies (lists of saints’ days and other holy dates). The exact contents of Benedict’s library is unknown, though it seems to have included a copy of a Bible used and illustrated by Cassiodorus, known as the Codex Grandior,; as well as theological works, a smattering of Greek philosophy and mathematics, and Cassiodorus’s encyclopaedias of ancient knowledge.
It was an impressive library for its day, though at best it contained some four to five hundred works.* This compares to perhaps two to three thousand volumes Cassiodorus had access to a century and a half earlier in his library, which itself was profoundly diminished from the vast collections of antiquity, including Alexandria’s library and its four hundred thousand manuscripts. Imagine what this meant to the inquiries of the second-century astronomer Claudius Ptolemy, who had a mountain of information at his disposal, compared to Bede. Working six hundred years later in his cold monastic cell at Jarrow, Bede had to make do with just a few treasured vellum scrolls tucked into wooden boxes to keep them from rotting in the dampness common to Northumbria.
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