Dionysius Exiguus ("Dennis the Small", "Dennis the Dwarf", "Dennis the Little" or "Dennis the Short") (c. 470 – c. 544) was a 6th-century monk born in Scythia Minor, modern Dobruja shared by Romania and Bulgaria. He was a member of the Scythian monks community concentrated in Tomis, the major city of Scythia Minor. Dionysius is best known as the "inventor" of the Anno Domini (AD) era, which is used to number the years of both the Gregorian calendar and the (Christianized) Julian calendar.
From about 500 C. C., Dionysius lived in Rome, where, as a learned member of the Roman 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.
The author of a continuation of Dionysius's Computus, writing in 616, described Dionysius as a "most learned abbot of the city of Rome", and the Venerable Bede accorded him the honorific abbas, which could be applied to any monk, especially a senior and respected monk, and does not necessarily imply that Dionysius ever headed a monastery. Indeed, Dionysius's friend Cassiodorus stated in Institutiones that he was still only a monk late in life.
Dionysius is best known as the inventor of the Anno Domini era, which is used to number the years of both the Gregorian calendar and the Julian calendar. He used it to identify the several Easters in his Easter table, but did not use it to date any historical event. When he devised his table, Julian calendar years were identified by naming the consuls who held office that year. He himself stated that the "present year" was "the consulship of Probus Junior", which he also stated was 525 years "since the incarnation of our Lord Jesus Christ". How he arrived at that number is unknown but there is evidence of the system he applied. He invented a new system of numbering years to replace the Diocletian years that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians. The Anno Domini era became dominant in Western Europe only after it was used by the Venerable Bede to date the events in his Ecclesiastical History of the English People, completed in 731.
There exists evidence that Dionysius' desire to replace Diocletian years (Diocletian persecuted Christians) with a calendar based on the incarnation of Christ was to prevent people from believing the imminent end of the world. At the time it was believed that the Resurrection and the end of the world would occur 500 years after the birth of Jesus. The current Anno Mundi calendar commenced with the creation of the world based on information in the Old Testament. It was believed that based on the Anno Mundi calendar Jesus was born in the year 5500 (or 5500 years after the world was created) with the year 6000 of the Anno Mundi calendar marking the end of the world. Anno Mundi 6000 (approximately AD 500) was thus equated with the resurrection of Christ and the end of the world. Since this date had already passed in the time of Dionysius, he therefore searched for a new end of the world at a later date. He was heavily influenced by ancient cosmology, in particular the doctrine of the Great Year that places a strong emphasis on planetary conjunctions. This doctrine says that when all the planets were in conjunction that this cosmic event would mark the end of the world. Dionysius accurately calculated that this conjunction would occur in about 1500 years after the life of Dionysius (in fact in May AD 2000). Dionysius then applied another astronomical timing mechanism based on precession of the equinoxes (that had only been discovered about six centuries earlier). Though incorrect, some oriental astronomers at the time believed that the precessional cycle was 24,000 years which included twelve astrological ages of 2,000 years each. Dionysius believed that if the planetary alignment marked the end of an age (i.e., the Pisces age), then the birth of Jesus Christ marked the beginning of the Age of Pisces 2,000 years earlier on the 25th of March (the former feast of Incarnation, now Annunciation, near the date of the Northern Hemisphere Spring Equinox and beginning of many yearly calendars from ancient times). He, therefore, deducted 2,000 years from the May 2000 conjunction to produce AD 1 for the incarnation of Christ even though modern scholars and the Roman Catholic Church acknowledge that the birth of Jesus was a few years earlier than AD 1.
In 525, Dionysius prepared a table of the future dates of Easter and a set of "arguments" explaining their calculation (computus) on his own initiative, at the request of Pope John I. 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 volume 67 of the 217 volume 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).
Dionysius 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).
Dionysius' tables were quickly adopted at Rome, and from this time the arguments between Rome and Alexandria regarding the correct date for the celebration of Easter came to an end – both used identical tables and hence observed the feast on the same day.
The epact (the age of the moon on 22 March) of all first decennovenal years was zero, making Dionysius the first known medieval Latin writer to use a precursor of the number zero. The Latin word nulla meaning no/none was used because no Roman numeral for zero existed. 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 "zeros" continued to be used by (among others) Bede, by whose extension of Dionysius Exiguus’ Easter table to a great Easter cycle all future Julian calendar dates of Easter Sunday were fixed unambiguously at last. However, in medieval Europe one had to wait as late as the second millennium to see the number zero itself come into use, although it had come into being around the year 600 in India.
Dionysius copied the last decennovenal cycle of the Cyrillian table ending with Diocletian 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', indicating 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 by 4 by 7 (decennovenal cycle × cycle of leap years × days in a week) fixed the Alexandrian cycle at 532 years, otherwise he would have stated such a simple fact.
Most of the British Church accepted the Dionysian tables after the Synod of Whitby in 664, which agreed that the old British method (the insular latercus) should be dropped in favor of the Roman one. Quite a few individual churches and monasteries refused to accept them, the last holdout finally accepting them during the early 10th century. The Church of the Franks (France) accepted them during the late 8th 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 (historians do not use a year zero). Because the anniversary of the Incarnation was 25 March, which was near Easter, a year that was 525 years "since the Incarnation" implied that 525 whole years were completed near that Easter. Consequently one year since the Incarnation would have meant 25 March 1, meaning that Dionysius placed the Incarnation on 25 March 1 BC. Because the birth of Jesus was nine calendar months later, Dionysius implied, but never stated, that Jesus was born 25 December 1 BC. One scholar, Georges Declerq (Declerq, 2002), thinks that Dionysius placed the Incarnation and Nativity in AD 1, basing his conclusion on the structure of Dionysius's Easter tables. In either case, Dionysius ignored his predecessors, who usually placed the Nativity in the year we now label 2 BC. In his 1605 thesis, the Polish historian Laurentius Suslyga was the first to suggest that Christ was actually born around 4 BC, deriving this from the chronology of Herod the Great, his son Philip the Tetrarch, and the daughter of Augustus, Julia. Having read Suslyga's work, Kepler noted that Christ was born during the reign of King Herod the Great, whose death he placed in 4 BC. Kepler chose this year because Josephus stated that a lunar eclipse occurred shortly before Herod's death. According to Josephus, Herod died in the year 4 or 3 BC.
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 (but not by the Church of Rome) at least as early as 311, and probably began during the first decade of the 4th 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.
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