Our father among the saints Dionysius Exiguus, also Dennis the Small, Dennis the Little or Dennis the Short - meaning humble, was a monastic theologian and canonist of the sixth century. An accomplished mathematician and astronomer, he is considered the inventor of the Christian calendar. His feast day is September 1.
Dionysius was born about the year 470 in Scythia Minor, now the area Dobruja that is shared by Romania and Bulgaria. He became a monk at a community of Scythian monks in Tomis, now Constanta. About 500, he moved to Rome where he led a monastery as abbot and was a member of the Roman Curia. Among his efforts, Dionysius translated 401 ecclesiastical canons from Greek into Latin. These included the apostolical canons and the decrees of the Ecumenical Councils held at Nicea, Constantinople, and Chalcedon, as well as the council at Sardis. He also translated a collection of the decretals of the bishops and popes of Rome from Siricus to Anastasius II.
He also translated a number of standard works from Greek to Latin, including the "Life of St. Pachomius", the "Instruction of St. Proclus of Constantinople" for the Armenians, the "De opificio hominis" of St. Gregory of Nyssa, and the history of the discovery of the head of St. John the Baptist.
Dionysius is best known for his work with the calendar, particularly, as the inventor of the Anno Domini era, that is reckoning the years from the incarnation, as is used now to number the years of the Christian calendars. He also developed tables for future dates of Pascha that returned the Christian West to the use of the principles used by the Church of Alexandria for observing the feast of Pascha.
The date of the repose of Dionysius is unknown but is believed to be about the year 544.