Dionysius Exiguus (Dennis the Little, meaning humble) (c. 470 – c. 540) was a 6th century Dacian monk born in Scythia Minor, in what is now the Dobruja, Romania.
Since 500 he lived in Rome, where, as a learned member of the Vatican's Curia, he translated from Greek into Latin 401 ecclesiastical canons, including the apostolical canons and the decrees of the councils of Nicaea, Constantinople, Chalcedon and Sardis, and also a collection of the decretals of the popes from Siricius to Anastasius II. These collections had great authority in the West and still guide church administrations. Dionysius also wrote a treatise on elementary mathematics. Bede and 'Felix' elevated him to an abbot (a leader of monks) even though Dionysius' friend Cassiodorus stated in Institutiones that he was still only a monk late in life.
In 525, Dionysius prepared a table of the future dates of Easter and a set of "arguments" explaining their calculation on his own initiative. Note well that only the first paragraphs of the first nine arguments are by Dionysius — arguments 10 to 16 as well as the additional paragraphs of eight and nine are later interpolations. Arguments 11 and 12 imply that these were interpolated in the year 675, shortly before Bede. He introduced his tables and arguments via a letter to a bishop Petronius (also written in 525) and added another explanatory letter (written in 526). These works in the voluminous Patrologia Latina also include a letter from Bishop Proterius of Alexandria to Pope Leo (written before 457). Though not named by Dionysius, this collection was recently called his Liber de Paschate (Book on Easter) by Audette.
He ignored the existing tables used by the Church of Rome, which were prepared in 457 by Victorius of Aquitaine , complaining that they did not obey Alexandrian principles, without actually acknowledging their existence. To be sure that his own tables were correct, he simply extended a set of tables prepared in Alexandria that had circulated in the West in Latin, but were never used in the West to determine the date of Easter (however, they were used in the Byzantine Empire, in Greek). The Latin tables were prepared by a subordinate of Bishop Cyril of Alexandria shortly before Cyril's death in 444. They covered a period of 95 years or five decennovenal (19-year) cycles with years dated in the Diocletian Era, whose first year was 285 (the modern historical year in progress at Easter). Diocletian years were advantageous because their division by 19 yielded a remainder equal to the year of the decennovenal cycle (1–19).
The epact (the age of the moon on 22 March) of all first decennovenal years was zero, making Dionysius the first known Latin medieval writer to use the number zero. The Latin word nulla meaning nothing was used because no Roman numeral for zero existed. Zero can probably be found in earlier Latin mathematical treatises, provided one looks for the word, not a symbol. To determine the decennovenal year, the Dionysian year plus one was divided by 19. If the result was zero (to be replaced by 19), it was represented by the Latin word nihil, also meaning nothing. Both uses of zero continued to be used by all later medieval computists (calculators of Easter), rendering false the common assumption that the number zero was unknown in Western Europe until its symbol (0) was obtained from Muslims during the twelfth century.
Dionysius copied the last decennovenal cycle of the Cyrillian table ending with Diocletion 247, and then added a new 95-year table with numbered Anni Domini Nostri Jesu Christi (Years of our Lord Jesus Christ) because, as he explained to Petronius, he did not wish to continue the memory of a tyrant who persecuted Christians. The only reason he gave for beginning his new 95-year table with the year 532 was that six years were still left in the Cyrillian table after the year during which he wrote. For the latter year he only stated that it was 525 years after the Incarnation of Christ, without stating when the latter event occurred in any other calendar. He did not realize that the dates of the Alexandrian Easter repeated after 532 years, despite his apparent knowledge of the Victorian 532-year 'cycle', stating only that Easter did not repeat after 95 years. He knew that Victorian Easters did not agree with Alexandrian Easters, thus he no doubt assumed that they had no bearing on any Alexandrian cycle. Furthermore, he obviously did not realize that simply multiplying 19 (the decennovenal cycle) by 4 (the cycle of leap years) by 7 (the week) fixed the Alexandrian cycle at 532 years, otherwise he would have stated such a simple fact. The years of Dionysius were used by Bede in his Ecclesiastical History of the English People (731), and due to Bede's great influence their use spread rapidly during the Middle Ages, and are still used by the modern Gregorian calendar.
No evidence exists that the Church of Rome accepted the Dionysian tables until the tenth century, although it is possible that they were accepted sometime during the sixth century. Most of the British Church accepted them after the Synod of Whitby in 664, although quite a few individual churches and monasteries refused to accept them, the last holdout finally accepting them during the early tenth century. The Church of the Franks (France) accepted them during the late ninth century under the tutelage of Alcuin, after he arrived from Britain.
Ever since the 2nd century, some bishoprics in the Eastern Roman Empire had counted years from the birth of Christ, but there was no agreement on the correct epoch — Clement of Alexandria (c. 190) and Eusebius of Caesarea (c. 320) wrote about these attempts. Because Dionysius did not place the Incarnation in an explicit year, competent scholars have deduced both AD 1 and 1 BC — most have selected 1 BC. (There was no zero year.) In either case, he ignored his predecessors, who usually placed the Nativity in the year we now label 2 BC. Kepler was the first to note that Christ was born during the reign of King Herod the Great (Matthew 2:1-18), whose death was placed in 4 BC by Josephus. The beginning of Dionysius' year was probably 25 March, the anniversary of the Incarnation ever since 25 December, nine months later, was chosen as the Nativity in the fourth century.
Although Dionysius stated that the First Council of Nicaea in 325 sanctioned his method of dating Easter, the surviving documents are ambiguous. A canon of the council implied that the Roman and Alexandrian methods were the same even though they were not, whereas a delegate from Alexandria stated in a letter to his brethren that their method was supported by the council. In either case, Dionysius' method had actually been used by the Church of Alexandria at least as early as 311, and probably began during the first decade of the fourth century, its dates naturally being given in the Alexandrian calendar . Thus Dionysius did not develop a new method of dating Easter. The most that he may have done was convert its arguments from the Alexandrian calendar into the Julian calendar. The resulting Julian date for Easter was the Sunday following the first Luna XIV (the 14th day of the moon) that occurred on or after the XII Kalendas Aprilis (21 March) (12 days before the first of April, inclusive). Nisan 14 was the date that Paschal lambs were slain (in late afternoon) until the destruction of the Second Temple in 70 prevented their continuing sacrifice, as well as the day when all leavened bread crumbs had to be collected and burned, hence Nisan 14 was the day of preparation for Passover. Alexandria may have chosen it because it was the day that Christ was crucified according to the Gospel of John (18:28, 19:14), in direct contradiction to the Synoptic Gospels (Matthew 26:17, Mark 14:12, and Luke 22:7), who state that he was crucified after he ate the Seder, his Last Supper. Then and now, the Seder was eaten after sundown at the beginning of Nisan 15. Because Dionysius's method of computing Easter used dates in the Julian calendar, it is also called the Julian Easter. This Easter is still used by almost all Orthodox churches. The Gregorian Easter still uses the same definition, but relative to its own solar and lunar dates.
- Bonnie Blackburn, Leofranc Holford-Strevens, "Calendars and chronology", The Oxford companion to the year (Oxford, 1999), 659-937.
- Georges Declercq, Anno Domini: The origins of the Christian era (Turnhout, 2000); idem, "Dionysius Exiguus and the introduction of the Christian era", Sacris Erudiri 41 (2002): 165-246.
- Dionysius Exiguus, Patrologia Latina 67 (works).
- Charles W. Jones, "Development of the Latin ecclesiastical calendar", in Bedae opera de temporibus (Cambridge, Mass., 1943), 1-122.
- Otto Neugebauer, Ethiopic astronomy and computus, Österreichische Akademie der Wissenschaften, philosophisch-historische klasse, sitzungsberichte, 347 (Vienna, 1979).
- Gustav Teres, "Time computations and Dionysius Exiguus", Journal for the history of astronomy, 15 (1984): 177-188.
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