POTTHAST, Bibliotheca historica medii ævi (Berlin, 1896), II, 1322-23; Bibliotheca hagiographica latina, ed. BOLLANDISTS, I, 478; WATTENBACH, Deutschlands Geschichtsquellen, I (7th ed., Berlin, 1904) 155; HEFELE, Geschichte der Einführung des Christenthums in Südwestl. Deutschland (Tübingen, 1837); LÜTOLF, Die Glaubensboten der Schweiz vor St. Gallus (Lucerne, 1871), 267 sqq.; LEO, Der hl. Fridolin (Freiburg im Br., 1886); HEER, St. Fridolin, der Apostel Alemanniens (Zürich, 1889); VON KNONAU, Nochmals die Frage St. Fridolin in Anzeiger für Schweizergesch. (1889), 377-81; SCHULTE, Beiträge zur Kritik der Vita Fridolini, Jahrbuch für Schweizergesch., XVIII (1893), 134-152.

Baring-Gould’s sources: Molanus and Greven in their additions to Usuardus. Canisius in his German Martyrology. Anglican and later Irish and Scottish Martyrologies. The Acts of Fridolin were preserved in a monastery on the Moselle, where they were found, and recast in a more ornate style, by a monk, Balther, in the beginning of the 12th cent. The story of this is rather curious. In the monastery of Sickingen there was no copy of the life of S. Fridolin, on account of the monastery having been destroyed by the Huns about 938. But Balther, a monk of Sickingen, happening to visit a monastery on the Moselle, which had been founded by S. Fridolin, found the life there. He asked for it, but the prior refused to give it him, so he learned it by heart, as well as he could, "partly carrying it away word for word, and partly gathering the subject-matter," after which he set to work and re-wrote it, incorporating the portions he knew by heart with that portion which he wrote in his own words. He says that he was puzzled to find that in the MS. the saint was called Fridhold, whereas at Sickingen they were wont to call him Fridolin. Fridhold was undoubtedly the ancient and most correct form of the name, and Fridolin is a diminutive.

Fridolin the Traveller was a native of Ireland, what his name there was is not known, as we only hear of him by his Teutonic appellation, signifying "Gentle Peace." His birth was illustrious, and he is usually said to have been the son of a king, but Balther merely says he was a person of distinguished piety. Having embraced the ecclesiastical state, he was raised to the priesthood, and preached with great zeal for some time in various parts of Ireland. Wishing to visit foreign countries, he passed over to France, and after preaching there, became a member of S. Hilary's monastery at Poitiers, where he remained for a considerable time, and was so much esteemed by the community, and the bishop and clergy, that he was elected abbot. He then completed an object which he had greatly at heart, the rebuilding of S. Hilary's Church, in which he was assisted by king Clovis, and by the bishop and the inhabitants; and he placed in it the remains of the saint, reserving a few portions of the relics [the bodily remains of a saint, or objects they used, kept with honor] for himself. During this time he was visited by two priests, relatives of his, who had been labouring as missionaries in Northumberland. Leaving them at Poitiers, and taking with him some of the relics of S. Hilary, Fridolin went to the east of France, and erected a monastery on the banks of the Moselle, which he dedicated to S. Hilary, and which was called Helera. Having remained there only as long as was necessary to complete that foundation, he built a church amidst the Vosges, likewise in honour of S. Hilary, perhaps that which was named Hilariacum, the modern S. Avold, in the Department of Moselle. Thence he proceeded to Strassburg, where also he erected a church under the same invocation. Next we find him at Coire, in the Grisons, and there likewise founding a Church of S. Hilary. While there, he inquired of the inhabitants if there were any island in the Rhine as yet uninhabited, and was informed there was one, of which, however, they could not give him a precise account. He went in search of it, and at length found the island of Sickingen, a few miles above Basle. When examining it for the purpose of discovering whether it were fit for the erection of a church, he was beaten and ill-treated by the inhabitants of the neighbouring district. But having obtained a grant of the island from the king, he founded a church, and a religious house for women, towards the endowment of which he got some lands from Urso, a nobleman of Glarus. Thenceforth he spent the remainder of his life at Sickingen, together with some disciples of his, of whom he formed a community, prior, it is said, to his having established the nunnery. He died there on the 6th of March, but in what year is not known. There are great doubts even as to the century in which he flourished; but it is most probable that he belonged to the latter part of the 7th century. Some writings have been attributed to the saint, but upon no sufficient authority. Many writers suppose that he arrived in France in the reign of Clovis I., but it is more probable that it was in the reign of Clovis III. According to Balther, Christianity seems to have been completely established in Ireland at the time of Fridolin's departure for France, and this representation does not suit the religious state of Ireland at the period when Clovis I. reigned. The holy expeditions of missionaries from Ireland to the continent, had not begun as early as the 6th century. Next comes the very remarkable circumstance of the priests, the nephews of Fridolin, coming from Northumberland. There were no Irish priests in Northumberland until the year 635.

S. Fridolin is regarded as the tutelar patron of the Canton of Glarus, which bears on its coat of arms a figure of the saint.