The majority of this article is taken from the excellent website Omnium Sanctorum Hiberniae, dedicated to preserving the memory of the Irish saints. This article concerns St. Kilian, also know as St, Coelan, an Irish island-saint of the 8th century, best known for his biography of the famous St. Brigid of Kildare. This extensive excerpt from the above mentioned website is itself an excerpt from the life of Coelan written by Canon O'Hanlon:
July 29 is the feastday of Saint Coelan, an eighth-century scholarly monk of Inis-cealtra, an island monastery of Lough Derg, County Clare. Its monastic school continued to produce a number of scholars over the centuries, and our Saint Coelan is said to have authored a metrical life of Saint Brigid of Kildare. Alas, the surviving manuscripts are not of good quality and the language used is not that of the saint's time, so scholars find some difficulties with the attribution to Saint Coelan. If nothing else though, Canon O'Hanlon's account below gives us an insight into some of the difficulties faced by the great 17th-century hagiologist, Father John Colgan, as he sought to collate the existing sources for the lives of Ireland's saints:
This highly gifted, esteemed and worthy religious had laboured so earnestly and so well, in his great and holy avocation to meet that God, whose service was the sole absorbing object of his life, that his future rewards were secured, even before they were fully realized. An elegant scholar, his mind was furthermore enlightened by the gifts of grace. It is much to be regretted, however, that his personal history has been so obscured, and that it has become so difficult of elucidation. The Natalis of St. Chelian or Coelan, a monk of Iniskeltra, occurs on the 29th of July, according to the Martyrology of Tallagh.
The Irish names Cillin, Cillen, Cillean, Cellin, and Cellen—bearing the same origin and signification—are often confounded; on account of verbal affinities, likewise, they have been classed with the names Coelan, Coelin and Coelen. These latter, however, are said to have a different derivation. The foregoing names are variously applied to our Irish Saints. The words, Cillin and Cillen, are diminutives deduced from Cill or Cell. Hence, in Latin, they are interpreted, by the expression, Cellanus. But, the words, Coelan, Coelen and Coelin are derived from the monosyllables, Coel, or Cail—or according to modern scholars, Caol—which signifies "slender," or "attenuated." As there is no letter K in the Irish language, its place is supplied by the consonant C, which before and after slender vowels, receiving the same pronunciation, as in other languages, should be accorded to the former letter. Hence, the aforesaid names, when Latinized, are variously expressed by these words, Cillinus, Killinus, Cellenus, Kellenus, Kilianus, Kilienus, Chilianus, Chilienus, &etc., also by Coelanus, Caolanus, Coelinus, Coelenus, Coelianus, Caelanus, &etc. In these words, also, oe, ai and ao are diphthongs.
The feast of St. Coelanus is entered in the Martyrology of Marianus O'Gorman, at the 29th of July. The Bollandists have a brief notice of Coelanus, at this same date, but they doubt his title to be enrolled in the Catalogue of the Saints. The Rev. Dr. Lanigan thinks, that Kilian lived not before the latter part of the eighth century, although he does not deem it worth his while, to enter upon a long discussion, regarding this saint. We may conjecture his birth to have taken place before or a little after the year 700; but, on this supposition, we have little evidence to guide us in making such a statement. Some six miles above the town of Killaloe, the Shannon expands into a noble lake. Anciently, it was called Loch Deirgheirt. This fine sheet of water extends ten miles in length, and it is about three miles across, at its greatest breadth. Many pretty islands stud its surface. One of these, formerly called Keltra, also Inis-Cealtra, Inish-Caltra, and sometimes Inniskeltair, bears likewise the name of Holy Island….
To St. Caimin has been generally ascribed the foundation of a monastery on Iniskeltair, early in the seventh century, and over which he presided to the period of his death, A.D. 653. A flourishing monastery—said to have been Benedictine in its form of rule—was thus established at a very early period, on the Island of Iniscaltra. Here, no doubt, a famous school had been conducted in after times. A succession of Abbots seems to have continued, until the place had been destroyed by Tomar, a Danish commander from Limerick, in the year 834.
It was afterwards restored, by the powerful and pious monarch of Ireland, Bryan Boroimhe [Brian Boru], a.d. 1007. The church on Holy Island, Lough Derg, is said to have been restored or remodelled by him in the eleventh century….
It is supposed, that St. Coelan had become a monk on the Island of Iniscaltra, and that he must have there lived for a considerable time. According to conjecture, he flourished about the end of the seventh or the beginning of the eighth century. At Iniscaltra, most probably, Kalian had received his education; which in a classical sense must have been an accomplished one. To him is attributed a very elegant metrical Life of St. Brigid. It was written in Latin Hexameter verse. Several Manuscript copies of this Life are supposed to be extant. As may be expected, in these there are various readings. Colgan has published a version, from a Monte Cassino Manuscript, collated with a copy, procured from the Vatican Library, and compared with other exemplars. Various emendations were deemed to be necessary. When Colgan had begun passing St. Brigid's Acts through the press, he received from the Rev. Father Bernard Egan, a learned Benedictine Abbot, and an Irishman, a certain fragment of that biography. At first, Colgan thought that poem began with lines, he there found; but, afterwards, he discovered that idea to have been a mistake. That copy he edited was drawn from one kept in the archives of Monte Cassino. Three other counterpart copies of those same Acts were procured by Colgan. One of them came from the Vatican Library, and another from the Library of His Eminence Cardinal Antonio Barberini, while a third was sent by the celebrated Franciscan Father, Luke Wadding. All of these copies were diligently collated by the editor, who found them severally mutilated and worn, abounding in false emendations of copyists, as also deformed with verbal transpositions and changes, to such a degree, that the sense of some verses could not be discovered, while the proper number of feet, and the required syllabic measure, were wanting in many other lines. But, to the collector's great industry, and by his observing closely the discrepancy of those copies, we are indebted for the publication of an old tract, which should have been very valuable, if it had not been disfigured through such negligence or incompetency of commentators or copyists. The editor endeavoured to follow the authorities he considered most authentic, in his several copies; for, he observed, that in many instances, the just number and measure of the verse could be found in some particular Manuscripts, while in others they were expressed, sometimes by abbreviations, again by a transposition of words, and often by some closing and arbitrary notation. The lines were frequently found so greatly mutilated, that they bore a prosaic rather than a metrical appearance. The editor detected so many omissions and licences, on the part of copyists, that he felt obliged to affix various marginal annotations to this poem. Through their incautiousness —a fruitful source of error in old documents—many transpositions of words were introduced, and certain synonymous terms were substituted for others besides, many abbreviations of doubtful meaning were found, and these left the sense imperfect. Even unaccountable caprice and mutilations caused some of the chapters to be acephalous or truncated, while some were altogether omitted. Certain lines are subjoined, from the Barbarini Manuscript, and which are wanting in that of Monte Cassino. Some breaks are discovered, likewise, in course of the narrative and structure of the poem. It was not possible always for the industry or research of either collator or editor, to repair so many imperfections or to restore so many omissions. Wherefore, Colgan only endeavoured to place in due order those words which seemed transposed, in certain passages, and cautiously to substitute others, in place of certain contracted words, doubtful in the reading, or which, through the error of copyists, were put for terms having a supposed affinity. Nor did the editor alter the poem, in the slightest tittle, except in those instances, where notable and obvious omissions of copyists left discrepancies between certain parts and lines, or where copyists so crudely amended them, that it could readily be conjectured, these emendations did not represent the original writer's words. For here and there, certain elegant and glowing phrases were found—especially in descriptive and metaphorical passages; then immediately afterwards, verses were maimed in prosodial number and quantity, while they were disfigured with blots. Colgan tells us, he published the poem, as he found it, changing nothing therein, but only the foregoing exceptional and false emendations. In Colgan's estimation, the author of this Sixth Life must have been this St. Coelan or Coelen.
The Bollandists hold a different opinion. Although many particulars, relating to St. Brigid, are found in the five first Lives, as published by Colgan, and which are missing in the Sixth; yet, the editor supposes this attributable to no other cause, than to the deplorable liberties taken by copyists with the original. Here and there, these have left many elisions and erasures; and, it can scarcely be doubted, but that they altogether pretermitted other matters. As that old and careful writer relates many of St. Brigid's Acts, omitted by others, and as it is indicated in the Prologue, according to Colgan's opinion, that he read her Lives, written by St. Ultan, Eleran, and Animosus; can it be supposed, he could have passed over so many accounts, faithfully related by various other writers, or that he would not have included several accounts, not given by them? The charges of omission, therefore, seem rather attributable to incompetent scribes, than to the author himself.
The writer of our illustrious saint's Sixth Life is supposed to have been no other than Choelian or Coelan, the monk of Iniskeltra. In the Barberini Manuscript of that same Life, there are two additional metrical Prologues, which precede this one descriptive of Ireland. These two Prologues consist of general observations, on the merits of the Saints, and extolling some great truths of religion, with prayers and fervent desires for future happiness, &c. It may be doubted, however, if these three Prologues had not been written at some time, subsequent to the composition of the metrical Life itself. Perhaps, they had been prefixed by a different writer, or by more than one composer. If we suppose the author of St. Brigid's Sixth Life to have been Coelanus of Inishcaltra, Colgan thinks he must have lived, towards the end of the seventh, or about the beginning of the eighth, century. Thus, from a metrical Life of St. Brigid, attributed to him, and from his own words, it is supposed, we may discover the age in which this writer flourished. For, in a Prologue to it, he relates, that St. Brigid's Acts had been written before, by Ultan, by Eleran, and by Animosus. An elegant metrical Prologue precedes those Acts of St. Brigid but, it has been doubted, if both had been composed, by the same author. St. Donatus, the Irish Bishop of Fiesole, who flourished in the ninth century, is said to have written that Prologue. The beautiful opening descriptive lines have been elegantly rendered into English verse, and more than one version has appeared. St. Ultan is supposed to have died A.D. 656, and St. Aleran, A.D. 664 or 665. Hence, Coelan must have lived after this latter year. In the Martyrology of Tallagh, the feast of St. Coelan of Iniskeltra is commemorated, at the 29th of July, and it must have been inserted after his death. St. Caolan is said to have lived contemporaneously with Oengus Mac Tiprait, who died A.D. 745. The circumstance of Chilien calling the mother of St. Brigid "a countess" seems to indicate a comparatively late period for this his assumed composition. In the Martyrology of Donegal, the feast of this saint is to be found, at the 29th of July. It is probable, that he died, about the middle of the eighth century.