Dionysius Exiguus

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Dionysius Exiguus

Roman scholar and theologian Dionysius Exiguus (c. 465 A.D.-c. 530 A.D.) is best known for his creation of a calendar that led to the modern Gregorian calendar. From his calendar stem the designations “B.C.” and “A.D.” Dionysius championed the system that is still used to determine the date of Easter, and his many translations and writings have influenced canon law and helped preserve early Church texts for study.

A Life Shrouded By History

Dionysius Exiguus, the man, is something of a mystery to modern scholars; Writing in Anno Domini: The Origins of the Christian Era, Georges Declercq argued that “the epithet ‘exiguus’ was adopted by Dionysius himself as a sign of intellectual humility, not because he was small of stature (‘the Short’).” Beyond this issue of nomenclature, the details of the early life and career of Dionysius have been lost over the centuries. Modern scholars do know that Dionysius originally came from Scythia—an area that in antiquity covered parts of presentday Russia, Ukraine, and Kazakhstan—where he was reputedly raised by a sect of Gothic monks before becoming a monk himself. A preface to one of his translations seems to indicate that Dionysius came from Scythia Minor, which today encompasses a portion of Romania that borders the Black Sea.

Regardless of his place of origin, sometime around 496 Dionysius came to Rome; he was by that time already a wellknown scholar who had been summoned by Pope Gelasius I to the city to organize the internal archives of the church, and, according to the New Catholic Encyclopedia, “to compile a collection of texts of incontestable worth and authenticity.” However, Dionysius did not arrive until after the Pope's death in November of 496. Because he was a respected scholar by then, it seems likely that Dionysius was born sometime around the 460s. The Catholic Encyclopedia noted that despite his origins, Dionysius was considered by contemporary Cassiodorus to be “a true Roman and thorough Catholic.” Dionysius seems to have remained in Rome for the remainder of his life. There, he lived as a monk; one sixth-century source claimed that Dionysius had been the abbot of a Roman monastery, but no evidence exists to support this assertion. Because modern scholars know that Dionysius constructed a set of Easter tables in the year 525, his death must fall at some time after that year; however, no evidence points to a date more specific than that.

Translated Important Church Documents

During his career, Dionysius worked in several fields of study. He translated many of the decrees issued by the Council of Nicaea, which created the first standard Christian doctrine; decrees by the Council of Constantinople, which created the first major revision of that doctrine; decrees by the First Council of Ephesus, which declared Mary to be the mother of God; and finally, decrees by the Council of Chalcedon, which established the difference between Jesus Christ the human and Jesus Christ the divine. These translations were published as three separate editions, including one dual Greek-Latin collection created at the behest of Hormisdas, who served as Pope from 514-523. The New Catholic Encyclopedia called this collection, the Dionysiana, “the first canonical collection worthy of the name.” Dionysius also collected letters written by fourthcentury Popes. These letters, together with his collections of council decrees, later served as important resources for the creators of canon, or church, law.

Dionysius also translated a number of texts describing the lives of saints, as well as theological works that recount early doctrinal debates among different groups within the Church. The New Catholic Encyclopedia claimed that “Dionysius's perfect knowledge of Greek and Latin is proved by his translations.”

In addition to translating important Church texts, Dionysius himself was a theologian who wrote on the early history of the Catholic Church. His biography in Science and Its Times stated that “he is credited with writing a collection of 401 ecclesiastical canons … that would become important historical documents about the early years of Christianity.”

Calculated Dates of Easter

According to the New Catholic Encyclopedia, “the entire work of Dionysius had but one purpose: the reconciliation of the Churches of the Orient and the West.” At the time of Dionysius, Christian doctrine was not yet standardized; the Christian world had divided into eastern and western branches due to disagreements on doctrinal matters.

One of Dionysius's efforts to reunite the divided Church related to the calculation of the dates of Easter, the most important Christian feast day, on which believers celebrate the resurrection of Jesus Christ from the dead. This date was one of much contention in the early Church, and was one cause of the split between the eastern and western branches of the Church. At the time, two methods competed for supremacy. One, the Alexandrine rule, had been created by the Council of Nicaea in 325. The other, used by the Church authorities in Rome at the time of Dionysius, declared that Easter must fall between March 25 and April 21 and relied on an 84-year cycle.

Dionysius was trained as a mathematician and an astronomer, and these skills surely helped him as he conducted studies into the calculation of dates. His work with the calendar stemmed from a request from Pope John I in 525 to extend the existing Easter tables for an additional 95 years. To do this, Dionysius chose to employ the Alexandrian method and to base his calculation on the Easter tables of St. Cyril, who had used the Alexandrian method, rather than those of Victorious of Aquitaine, which employed the cycle then endorsed by the Roman Church.

A number of bishops asked Dionysius to explain this decision, and Dionysius responded to this request in the preface to his Book on Easter Reckoning, as quoted by Declercq. Declercq noted that Dionysius believed firmly that the Council of Nicaea endorsed the Alexandrian method, and summarized Dionysius's explanation of the criteria of that method thus: “The beginning of the first lunar month, Nisan, from 8 March to 5 April inclusive; the lunar limits 15-21 for Easter Sunday; the theory of the spring equinox on 21 March as the earliest possible date for the Paschal [spring] or 14th moon; the calendar limits for the Paschal full moon (21 March to 18 April) and those for the festival of Easter itself (22 March to 25 April).”

These criteria dictated that Easter would occur on the first Sunday following the 14th day of the lunar cycle—the full moon—that falls on or after the spring equinox. Despite the controversy caused by Dionysius's use of this method, his tables noting the dates of Easter for the years 532-626 stood. Western Christianity still calculates the date of Easter using this method, showing the lasting impact of Dionysius's work.

Created the Christian Era

In the course of determining the date of Easter, Dionysius also created the Christian Era calendar, commonly used today and recognizable by its B.C./A.D. (“Before Christ”/“Anno Domini”) designations. The calendar in the era of Dionysius differed from the modern calendar. Instead of relying on the modern Gregorian calendar, people of Dionysius's time determined the year using the Julian calendar. This calendar was created by famed Roman statesman Julius Caesar in an attempt to correct the highly inaccurate Roman calendar of his day. (The Gregorian calendar, introduced in 1582, would later perfect the Julian system's minor errors, primarily regarding the placement of leap days.) This calendar numbered years commencing from either the foundation of the city in Rome, or from the first year of the reign of the Roman Emperor Diocletian; using the former system, the year in which Dionysius's Easter tables would take effect would be called 1285, and by the later, 248.

The Diocletian dating system was at the fore in the era of Dionysius. Preferring not to memorialize Diocletian, who had been a somewhat tyrannical emperor and had persecuted Christians, by basing the calendar upon his reign, Dionysius decided to renumber the years. In The Oxford Companion to the Year: An Exploration of Calendar Customs and Time Reckoning, Bonnie Blackburn and Leofranc Holford-Strevens quoted Dionysius as stating that he wished to date the year “from the Incarnation of our Lord Jesus Christ, in order that the beginning of our hope should be better known to us and the cause of our recovery, that is the Passion of our Redeemer, should shine forth more clearly.” Dionysius thus renumbered the years beginning with the incarnation of Jesus Christ, beginning with the year 1 as the Roman numbering system had no way to indicate a zero. This meant that his Easter tables began with the year 532, instituting the Christian Era (also called the Incarnation Era) still used for reckoning the number of the year.

However, Dionysius incorrectly calculated the year of Christ's birth. Both ancient and modern scholars placed this event some time between 6 and 2 B.C. The reason for Dionysius's error is unclear. Some scholars have speculated that the inaccuracy may have stemmed from Dionysius placing the first day of the year in September rather than January; basing the indicator of the year on the number of elapsed years, rather than noting the date of the current year; and considering the incarnation to be the moment of birth, rather than the moment of conception. Alternatively, Dionysius may have simply misinterpreted a document listing the names of consuls, for whom the Romans named the year at the time of Christ, and made some minor miscalculation that resulted in the date shift.


The legacy of Dionysius Exiguus is evident throughout the world. His dating system, incorporated into the standard Gregorian calendar, is the most common reckoning of the year around the globe. The Alexandrian rule of calculating the date of Easter, introduced by Dionysius, remains the method used by Western Christianity to set this feast day. Although the details of his life are unknown, the effects of that life affect human society at all levels.


Blackburn, Bonnie, and Leofranc Holford-Strevens, The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-reckoning, Oxford University Press, 1999.

Declercq, Georges, Anno Domini: The Origins of the Christian Era, Brepols, 2000.

New Catholic Encyclopedia, Gale, 2002.

Science and Its Times, Vol. 1: 2000 B.C. – 700 A.D., Gale Group, 2001.


“Dionysius Exiguus,” Catholic Encyclopedia, http://www.newadvent.org/cathen/05010b.htm (November 26, 2007).

Dionysius Exiguus

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Dionysius Exiguus


Scythian Theologian, Mathematician, and Astronomer

Dionysius Exiguus, a Roman theologian, mathematician, and astronomer, is known for inventing a Christian calendar that was later incorporated into the currently used Gregorian calendar. In addition to providing calculations for determining the date of Easter, Dionysius's calendar is notable for establishing its starting point from the birth of Jesus Christ, thus introducing the designations b.c. and a.d.

Little is known of Dionysius's early life. It is documented, however, that he arrived in Rome about the time of the death, in 496, of Pope Gelasius I, who had summoned him to organize the official archives of the church hierarchy. The Roman Empire was in ruins, and the city of Rome itself was dilapidated and nearly deserted.

A trained mathematician and astronomer, as well as a master theologian, Dionysius spent his days working at a complex now known as the Vatican. He wrote church canons and spent a great deal of time thinking about how to make order of time itself. He worked as a church scholar for many years and in 525, at the request of Pope John I, he began work on the calculations that would become the basis of the Gregorian calendar centuries later. At the time, the Julian calendar, devised by Julius Caesar (100-44 b.c.), was used as the working calendar of the Church. One of the most problematic calculations for these Roman timekeepers was figuring out where the holy days fell, especially Easter.

Pope John I asked Dionysius to calculate the dates upon which future Easters would fall. The Church had adopted a formula some 200 years earlier stating that Easter should fall on the first Sunday after the first full moon following the spring equinox. Dionysius carefully studied the positions of the Moon and Sun and was able to produce a chart noting the dates of upcoming Easters, beginning in the year 532. This compilation was received with some controversy, but was accepted. At that time, most people used the year designated as either 1285, dated from the founding of Rome, or 248, based on a calendar that began with the first year of the reign of Emperor Diocletian.

Dionysius defended his decision, suggesting that his calculation was taken from the reputed birth date of Jesus Christ. 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." The new Easter charts reflected this preference, which began with anno Domini nostri Jesu Christi DXXXII, or a.d. 532. Dionysius's system used the designations a.d. (after Christ's birth) and b.c. (before Christ). However, Dionysius miscalculated Christ's birth as a.d. 1, as there was no zero value in the Roman numeral system, instead of 4 or 5 b.c. (before Christ) as is now generally accepted. The sixteenth-century pope Gregory III later adapted and incorporated the Julian calendar, with its problem of loosing entire days over time, into what became known as the Gregorian calendar. This calendar is the most popular and widely used in the world today.

In addition to his skill as a mathematician and astronomer, Dionysius was highly regarded as a theologian. He is credited with writing a collection of 401 ecclesiastical canons or scriptures that would become important historical documents about the early years of Christianity. He is also responsible for compiling an important collection of decrees written by Pope Siricius (344?-399) and Pope Anastasius II (?-498). He translated many works from Greek into Latin, thus preserving many important documents for later scholars.


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