Baring-Gould’s sources: Gallican and Roman Martyrologies. Authority:—Various editions of the life of S. Regulus, the most ancient probably of the 9th cent. The cathedral of Senlis was burnt in that century, and together with it perished all its archives. Those lives extant were written from tradition after this fire. S. Regulus is called in France S. Rieul .

S. Regulus was a native of Argos. Hearing of the miracles wrought at Ephesus by the Beloved Disciple, S. John the Divine, he went thither, and was converted by him. The Blessed Apostle, admiring his virtue, ordained him, and kept him by him as a dear friend. But persecution soon parted the pupil from his master, for S. John was exiled to Patmos. After a while, Regulus, hearing that S. Dionysius, the Areopagite, was leaving Rome to bear the gospel into lands that knew not Christ, followed him, and S. Denys took with him Rusticus for his deacon, Eleutherius as subdeacon, Regulus, Lucian, Eugenius, and others. Regulus was appointed bishop of Arles, where he found a colony of Christians which had been formed by S. Trophimus. According to the legend, one day, as Regulus was saying Mass, after he had recited in the canon the names of SS. Peter and Paul, he added, without thinking of what he was saying, "also the blessed martyrs, Denys, Rusticus, and Eleutherius," and thereupon saw three doves descend on the altar, with these three names in bloody characters inscribed on their breasts. Knowing that these three blessed apostles must be dead, he went to Paris to gather up their sacred relics [the bodily remains of a saint, or objects they used, kept with honor], having first confided the care of his church to a bishop named Felicissimus. On arriving, he went to the village of Châton, where he met a lady, named Catulla, who had secretly buried the bodies of the martyrs. Regulus celebrated the holy Sacrifice over their grave, and Catulla built a chapel of wood on the spot. This was the chapel which S. Genoveva afterwards rebuilt in stone (vol. i. p. 50). Regulus then left Paris, and took the road to Senlis. Passing through Louvres, six leagues from Paris, he overthrew an idol of Mercury, which he found there, preached to the people, and built a chapel, which was afterwards dedicated to the Blessed Virgin. Regulus then undertook the conversion of the people of Senlis, which he happily effected. Then he betook himself to Beauvais, and the story goes that as the frogs in the marshes disturbed him whilst preaching he forbade them all croaking with the exception of one. He is said to have died in 130, during the reign of Hadrian, after having laboured forty years in different missions. So far the legendary life, which is destitute of respect as history. In all probability two saints have been run into one, a S. Regulus of Arles, the successor of S. Trophimus, and a S. Regulus of Senlis, who lived in the end of the third century, and died in the early part of the fourth, for he is spoken of as a companion of saints who certainly lived at that period.

In art S. Regulus or Rieul is represented with frogs at his side, or releasing captives from their chains.