Bishop of Paris, and martyr. Born in Italy, nothing is definitely known of the time or place, or of his early life. His feast is kept on 9 October. He is usually represented with his head in his hands because, according to the legend, after his execution the corpse rose again and carried the head for some distance. That, however, while still very young he was distinguished for his virtuous life, knowledge of sacred things, and firm faith, is proved by the fact that Pope Fabian (236-250) sent him with some other missionary bishops to Gaul on a difficult mission. The Church of Gaul had suffered terribly under the persecution of the Emperor Decius and the new messengers of Faith were to endeavour to restore it to its former flourishing condition. Denis with his inseparable companions, the priest Rusticus and the deacon Eleutherius, arrived in the neighbourhood of the present city of Paris and settled on the island in the Seine. The earliest document giving an account of his labours and of his martyrdom (Passio SS. Dionsyii, Rustici et Eleutherii), dating from the end of the sixth or the beginning of the seventh century and wrongly attributed to the poet Venantius Fortunatus, is interwoven with much legend, from which, however, the following facts can be gleaned.
On the island in the Seine Denis built a church and provided for a regular solemnization of the Divine service. His fearless and indefatigable preaching of the Gospel led to countless conversions. This aroused the envy, anger and hatred of the heathen priests. They incited the populace against the strangers and importuned the governor Fescenninus Sisinnius to put a stop by force to the new teaching. Denis with his two companions were seized and as they persevered in their faith were beheaded (about 275) after many tortures. Later accounts give a detailed description of the confessors' sufferings. They were scourged, imprisoned, racked, thrown to wild beasts, burnt at the stake, and finally beheaded. Gregory of Tours simply states: "Beatus Dionysius Parisiorum episcopus diversis pro Christi nomine adfectus poenis praesentem vitam gladio immente finivit" (Hist. Franc. I, 30). The bodies of the three holy martyrs received an honourable burial through the efforts of a pious matron named Catulla and a small shrine was erected over their graves. This was later on replaced by a beautiful basilica (egregium templum) which Venantius celebrated in verse (Carm. I, ii).
From the reign of King Dagobert (622-638) the church and the Benedictine monastery attached to it were more and more beautifully adorned; the veneration of St. Denis became by degrees a national devotion, rulers and princes vying with one another to promote it. This development is due in no small degree to an error prevailing throughout the Middle Ages, which identified St. Denis of Paris with St. Dionysius the Areopagite, and with the Pseudo-Dionysius, the composer of the Areopagitic writings. The combining of these three persons in one was doubtless effected as early as the eighth or perhaps the seventh century, but it was only through the "Areopagitica" written in 836 by Hilduin, Abbot of Saint-Denis, at the request of Louis the Pious, that this serious error took deep root. The investigations of Launoy first threw doubt on the story and the Bollandist de Bye entirely rejected it. Hilduin was probably deceived by the same apocryphal Latin and Greek fictions. The possession of the Areopagitic writings (since 827 in Saint-Denis) strengthened his conviction of this truth. Historiographers of the present day do not dispute this point. All attempts of Darras, Vidieu, C. Schneider, and others to throw some light on the subject have proved fruitless.
Source: Catholic Encyclopedia - NewAdvent.org