Celtic Christianity or Insular Christianity refers broadly to certain features of Christianity that were common, or held to be common, across the Celtic-speaking world during the Early Middle Ages. "Celtic Christianity" has been conceived of with differing levels of specificity: some writers have thought of it as a distinct "Celtic Church" uniting the Celtic peoples and distinguishing them from the "Roman" Catholic Church, while others classify it as simply a set of distinctive practices occurring in those areas. Scholars now reject the former notion, but note that there were certain traditions and practices used in both the Irish and British churches but not in the wider Christian world. These include a distinctive system for determining the dating of Easter, a style of monastic tonsure, a unique system of penance, and the popularity of going into "exile for Christ". Additionally, there were other practices that developed in certain parts of the Celtic world, but which are not known to have spread beyond a particular region. Rituals associated with Celtic Christianity are now almost completely lost, though two books, the Bobbio and the Stowe Missals, contain the Irish Ordinary of a daily Mass in late, Romanized form.
The term "Celtic Church" is deprecated by many historians as it implies a unified and identifiable entity entirely separate from the mainstream of Western Christendom. Others prefer the term "Insular Christianity". As Patrick Wormald explained, “One of the common misconceptions is that there was a ‘Roman Church’ to which the ‘Celtic’ was nationally opposed.” Celtic-speaking areas were part of Latin Christendom as a whole at a time in which there was significant regional variation of liturgy and structure with a general collective veneration of the Bishop of Rome that was no less intense in Celtic areas.
Nonetheless, it is possible to talk about the development and spread of distinctive traditions, especially in the sixth and seventh centuries. Some elements may have been introduced to Ireland by the Briton St. Patrick, later others spread from Ireland to Britain with the Irish mission system of Saint Columba. The histories of the Irish, Welsh, Scots, Breton, Cornish, and Manx Churches diverge significantly after the eighth century (resulting in a great difference between even rival Irish traditions).
"Celtic Christianity" has been conceived of in different ways at different times. Writings on the topic frequently say more about the time in which they originate than the historical state of Christianity in the early medieval Celtic-speaking world, and many notions are now discredited in modern academic discourse. One particularly prominent feature ascribed to Celtic Christianity is that it is supposedly inherently distinct from – and generally opposed to – the Catholic Church. Other common claims are that Celtic Christianity denied the authority of the Pope, was less authoritarian than the Catholic Church, more spiritual, friendlier to women, more connected with nature, and more comfortable dealing with the ancient Celtic religion. One view, which gained substantial scholarly traction in the 19th century, was that there was a "Celtic Church", a significantly organized Christian body or denomination uniting the Celtic peoples and separating them from the "Roman" church of continental Europe. Others have been content to speak of "Celtic Christianity" as consisting of certain traditions and beliefs intrinsic to the Celts.
However, modern scholars have identified problems with all of these claims, and find the term "Celtic Christianity" problematic in and of itself. The idea of a "Celtic Church" is roundly rejected by modern scholars due to the lack of substantiating evidence. Indeed, there were distinct Irish and British church traditions, each with their own practices, and there was significant local variation even within the individual Irish and British spheres. While there were some traditions known to have been common to both the Irish and British churches, these were relatively few. Even these commonalities did not exist due to the "Celticity" of the regions, but due to other historical and geographical factors. Additionally, the Christians of Ireland and Britain were not "anti-Roman"; the authority of Rome and the papacy were venerated as strongly in Celtic areas as they were in any other region of Europe. Caitlin Corning further notes that the "Irish and British were no more pro-women, pro-environment, or even more spiritual than the rest of the Church."
Corning notes that scholars have identified three major strands of thought that have influenced the popular conceptions of Celtic Christianity. The first arose in the English Reformation, when the Church of England declared itself separate from the Catholic Church. Protestant writers of this time popularized the idea of an indigenous British Christianity that opposed the foreign "Roman" church and was purer (and proto-Protestant) in thought. The English church, they claimed, was not forming a new institution, but casting off the shackles of Rome and returning to its true roots as the indigenous national church of Britain. Ideas of Celtic Christianity were further influenced by the Romantic movement of the 18th century, in particular Romantic notions of the noble savage and the intrinsic qualities of the "Celtic race". The Romantics idealized the Celts as a primitive, bucolic people who were far more poetic, spiritual, and freer of rationalism than their neighbors. The Celts were seen as having an inner spiritual nature that shone through even after their form of Christianity had been destroyed by the authoritarian and rational Rome. In the 20th and 21st centuries, these ideas were combined with appeals by certain modern churches and neo-pagan and New Age groups seeking to recover something of ancient spirituality that is felt to be missing from the modern world. For these groups Celtic Christianity becomes a cipher for whatever is lost in the modern religious experience. Corning notes that these notions say more about modern desires than about the reality of Christianity in the Early Middle Ages, however.
Christianity reached Britain by the third century of the Christian era, the first recorded martyrs in Britain being St. Alban and Aaron and Julius, citizens of Caerleon, during the reign of Diocletian. Gildas dated the faith's arrival to the latter part of the reign of Tiberius.
Christianisation intensified with the legalization of the Christian religion under Constantine in the early 4th century and its promotion by subsequent Christian emperors, but in 407 the Empire withdrew its legions from the province to defend Italy from Visigothic attacks in which the city of Rome would be sacked in 410. The legions did not permanently return to Britain, Roman tax and army influence ended on the isle and, with the decline of Roman imperial political influence, Insular Christianity retained distinct traditions and practices through the era of Church Councils. Clerics such as Germanus of Auxerre accused some British bishops of the heresy of Pelagianism and sought their removal from office.
According to hagiographies written some centuries later, Illtud and his pupils David, Gildas, Paul Aurelian, Samson and Deiniol from the next generation, were leading figures in sixth-century Britain. Some of them were also active in Brittany. Others who influenced the development of British Christianity include Dubricius, Cadoc, Petroc, Piran, Ia and Kentigern (also known as Mungo).
A monastery-centred establishment seems to have grown up in sixth-century Britain, though our knowledge of this period there is limited. There may have been interaction with Ireland at this time, perhaps partly brought about by a very severe plague in Ireland in 548/9, only a few years after the extreme weather events of 535–536. However, Bede speaks of "the monastery of Bangor, in which, it is said, there was so great a number of monks, that the monastery being divided into seven parts, with a superior set over each, none of those parts contained less than three hundred men, who all lived by the labour of their hands."
At the end of the 6th century, the face of Christianity in Britain was forever changed by the Gregorian mission. In this endeavour, Pope Gregory I sent a group of clerics headed by the monk Augustine to convert the Anglo-Saxons to Christianity and to establish new churches and dioceses in their territory. Gregory intended for Augustine to become the metropolitan archbishop over all of southern Britain, including over the bishops already serving among the Britons. Augustine met British bishops in a series of conferences in which he attempted to assert his authority and persuade them to abandon certain customs that conflicted with Roman practice. However, these conferences failed to reach any agreement.
The only surviving account of Augustine's meetings with the British clergy is that in the Historia ecclesiastica gentis Anglorum of the Northumbrian writer Bede. According to Bede, some bishops and other representatives of the nearest province of the Britons met Augustine at a location at the border of the Kingdom of Kent, which was thereafter known as Augustine's Oak. Augustine tried to convince the delegates to join his proselytizing efforts, and to reform certain of their customs, particularly their Easter computus. Though impressed with the newcomer, the Britons asserted that they could not agree to his demands without conferring with their people. They then withdrew until a fuller assembly could be arranged.
Bede relates an anecdote that the British bishops consulted a wise hermit as to how to respond to Augustine when he arrived for the second council. The hermit replied that they should make the decision based on Augustine's own conduct. If he should rise to greet them at the council, they would know him as a humble servant of Christ and should submit to him, but if he arrogantly kept his seat, they should reject him. As it happened, Augustine did not rise at the council, causing outrage. Augustine offered to allow the Britons to maintain most of their customs if they made three concessions: they should adopt the Roman method of calculating Easter's date, reform their baptismal rite, and join the missionary efforts among the Saxons. The Britons rejected all of these, and, adds Bede, refused to recognize Augustine's authority over them. Bede reports that Augustine is said to have then delivered a prophecy that the British church's failure to proselytize the Saxons would bring them war and death at their hands. He gives the Battle of Chester, at which many British clergy were said to have been killed by the pagan King Æthelfrith of Northumbria, as the fulfillment of this prophecy.
Thereafter, "Celtic" customs were often seen as conflicting with the Roman customs adopted in most of the Anglo-Saxon kingdoms. The most significant contention was over the Easter dating, which of all the points of disagreement would have produced the most obvious signs of disunity for observers. Under the two systems Easter did not generally coincide, and as such it would be matter of course for Christians following one system to be solemnly observing Lent while others were celebrating the feast of the Resurrection. Indeed, this is noted as occurring in the household of King Oswiu of Northumbria, whose kingdom had been evangelized by both Irish and Roman missionaries. The other custom that consistently drew the ire of adherents to Roman custom was the Celtic tonsure. There is no indication that Augustine himself raised this issue, but it does appear in several other sources, which invariably connect it to the Celtic dating for Easter. John Edward Lloyd suggests that the primary reason for the British bishops' rejection of Augustine, and especially his call for them to join his missionary effort, may have been his claim to sovereignty over them. It may have been difficult for them to accept the supremacy of a see so deeply entwined with the power of Anglo-Saxon Kent.
A sense of the independent apostolic succession of the British church endured in the Norman era as the claim that Christianity in Britain had been founded by Saint Joseph of Arimathea at Glastonbury and that King Arthur, supposedly buried in Glastonbury Abbey, had been the sole upholder of the faith after the fall of Rome. The legend that Jesus himself visited Britain is referred to in "And did those feet in ancient time", by William Blake in 1804, and in the hymn "Jerusalem", with music written by C. Hubert H. Parry in 1916. Such ideas were used by mediaeval anti-Roman movements such as the Lollards and followers of John Wyclif.
By the early fifth century the religion had spread to Ireland, which had never been part of the Roman Empire. The highly successful 5th-century mission of Saint Patrick established churches in conjunction with civitates like his own in Armagh; small enclosures in which groups of Christians, often of both sexes and including the married, lived together, served in various roles and ministered to the local population.
Within a few generations of the arrival of the first missionaries the monastic and clerical class of the isle had become fully integrated with the culture of Latin letters. Besides Latin, Irish ecclesiastics developed a written form of Old Irish. During the late 5th and 6th centuries true monasteries became the most important centres: in Patrick's own see of Armagh the change seems to have happened before the end of the 5th century, thereafter the bishop was the abbot also. Finnian of Clonard is said to have trained the Twelve Apostles of Ireland at Clonard Abbey.
In the sixth and seventh centuries, Irish monks established monastic institutions in parts of modern-day Scotland (especially Columba, also known as Colmcille or, in Old Irish, Colum Cille), and on the continent, particularly in Gaul (especially Columbanus). Monks from Iona under St. Aidan founded the See of Lindisfarne in Anglo-Saxon Northumbria in 635, whence Celtic practice heavily influenced northern England.
The achievements of insular art, in illuminated manuscripts like the Book of Kells, high crosses, and metalwork like the Ardagh Chalice remain very well known, and in the case of manuscript decoration had a profound influence on Western medieval art. The manuscripts were certainly produced by and for monasteries, and the evidence suggests that metalwork was produced in both monastic and royal workshops, perhaps as well as secular commercial ones. Irish monks also founded monasteries across the continent, exerting influence greater than many more ancient continental centres. The first issuance of a papal privilege granting a monastery freedom from episcopal oversight was that of Pope Honorius I to Bobbio Abbey, one of Columbanus's institutions.
At least in Ireland, the monastic system became increasingly secularised from the 8th century, as close ties between ruling families and monasteries became apparent. The major monasteries were now wealthy in land and had political importance. On occasion they made war either upon each other or took part in secular wars - a battle in 764 is supposed to have killed 200 from Durrow Abbey when they were defeated by Clonmacnoise. From early periods the kin nature of many monasteries had meant that some married men were part of the community, supplying labour and with some rights, including in the election of abbots (but obliged to abstain from sex during fasting periods). Some abbacies passed from father to son, and then even grandsons. A revival of the ascetic tradition came in the second half of the century, with the culdee or "clients (vassals) of God" movement founding new monasteries detached from family groupings.
Saxon connections with the greater Latin West led to papal preferment and brought the Celtic-speaking peoples into closer contact with the orthodoxy of the councils. The customs and traditions particular to Insular Christianity became a matter of dispute, especially the matter of the proper calculation of Easter. Synods were held in Ireland, Gaul, and England (e.g. the Synod of Whitby) but a degree of variation continued in Britain after the Ionan church accepted the Roman date.
The Easter question was settled at various times in different places. The following dates are derived from Haddan and Stubbs: South Ireland, 626-8; North Ireland, 692; Northumbria (converted by Celtic missions), 664; East Devon and Somerset, the Celts under Wessex, 705; the Picts, 710; Iona, 716-8; Strathclyde, 721; North Wales, 768; South Wales, 777. Cornwall held out the longest of any, perhaps even, in parts, to the time of Bishop Aedwulf of Crediton (909).
Pan-Celtic traditions 
Caitlin Corning identifies four customs that were common to both the Irish and British churches but not used elsewhere in the Christian world.
Easter calculation 
The Irish and British churches shared a computus, or method of dating Easter, that was distinct from the system used on the Continent. This is an example of the conservatism, even archaism of Celtic Christianity. Calculating the proper date of Easter was (and is) a complicated process involving a lunisolar calendar. Various tables were produced in antiquity that attempted to calculate Easter for a series of years. Insular Christianity used a calculation table (Celtic-84) that was similar to one approved by Saint Jerome. However, by the sixth and seventh centuries it had become obsolete and had been replaced by those of Victorius of Aquitaine and, more accurately, those of Dionysius Exiguus. As the Celtic world established renewed contact with the Continent it became aware of the divergence; the first clash over the matter came in Gaul in 602, when Columbanus resisted pressure from the local bishops to conform. Most groups, like the southern Irish, accepted the updated tables with relatively little difficulty, with the last significant objectors being the monks from the monastery of Iona and its many satellite institutions. For example, the southern Irish accepted the common Easter calculation at the Synod of Mag Léne around 630, as did the northern Irish at the Council of Birr around 697, and Northumbria with the Synod of Whitby in 664. Nonetheless, in 716 Iona converted its practice.
Monastic tonsure 
All monks of the period, and apparently most or all clergy, kept a distinct tonsure, or method of cutting one's hair, to distinguish their social identity as men of the cloth. In Ireland men otherwise wore longish hair, and a shaved head was worn by slaves.
The prevailing "Roman" custom was to shave a circle at the top of the head, leaving a halo of hair or corona; this was eventually associated with the imagery of Christ's Crown of Thorns. The early material referring to the Celtic tonsure emphasizes its distinctiveness from the Roman alternative and invariably connects its use to the Celtic dating of Easter. Those preferring the Roman tonsure considered the Celtic custom extremely unorthodox, and associated it with the form of tonsure worn by the heresiarch Simon Magus. This association appears in a 672 letter from Saint Aldhelm to King Geraint of Dumnonia, but it may have been circulating since the Synod of Whitby. The tonsure is also mentioned in a passage, probably of the 7th century but attributed wrongly to Gildas: "Britones toti mundo contrarii, moribus Romanis inimici, non solum in misa sed in tonsura etiam" ("Britons are contrary to the whole world, enemies of Roman customs, not only in the Mass but also in regard to the tonsure").
The exact shape of the Irish tonsure is unclear from the early sources, although they agree that the hair was in some way shorn over the head from ear to ear. In 1639 James Ussher suggested a semi-circular shape, rounded in the front and culminating at a line between the ears. This suggestion was accepted by many subsequent writers, but in 1703, Jean Mabillon put forth a new hypothesis, claiming that the entire forehead was shaven back to the ears. Mabillon's version was widely accepted, but contradicts the early sources. In 2003 Daniel McCarthy suggested a triangular shape, with one side between the ears and a vertex towards the front of the head. The Collectio canonum Hibernensis cites the authority of Saint Patrick as indicating that the custom originated with the swineherd of Lóegaire mac Néill, the king who opposed Patrick.
In Ireland a distinctive form of penance developed, where confession was made privately to a priest, under the seal of secrecy, and where penance was given privately and ordinarily performed privately as well. Certain handbooks were made, called “penitentials”, designed as a guide for confessors and as a means of regularising the penance given for each particular sin.
In antiquity, penance had been a public ritual. Penitents were divided into a separate part of the church during liturgical worship, and they came to mass wearing sackcloth and ashes in a process known as exomologesis that often involved some form of general confession. There is evidence that this public penance was preceded by a private confession to a bishop or priest (sacerdos), and it seems that, for some sins, private penance was allowed instead. Nonetheless, penance and reconciliation was prevailingly a public rite (sometimes unrepeatable), which included absolution at its conclusion.
The Irish penitential practice spread throughout the continent, where the form of public penance had fallen into disuse. Saint Columbanus was credited with introducing the medicamenta paentitentiae, the “medicines of penance”, to Gaul at a time when they had come to be neglected. Though the process met some resistance, by 1215 the practice had become established as the norm, with the Fourth Lateran Council establishing a canonical statute requiring confession at a minimum of once per year.
A final distinctive tradition common across the Celtic world was the popularity of peregrinatio pro Christo, or "exile for Christ". The term peregrinatio is Latin, and referred to the state of living or sojourning away from one's homeland in Roman law. It was later used by the Church Fathers, in particular Saint Augustine of Hippo, who wrote that Christians should live a life of peregrinatio in the material world while awaiting the Kingdom of God. Augustine's version of peregrinatio spread widely throughout the Christian church, but it took two additional unique meanings in Celtic countries.
In the first sense, the Celtic penitentials prescribed permanent or temporary peregrinatio as penance for certain infractions. Additionally, there was a tradition of undertaking a voluntary peregrinatio pro Christo, in which individuals permanently left their homes and put themselves entirely in God's hands. In the Irish tradition there were two types of such peregrinatio, the "lesser" peregrinatio, involving leaving one's home area but not the island, and the "superior" peregrinatio, which meant leaving Ireland for good. Most peregrini or exiles of this type were seeking personal spiritual fulfillment, but many became involved in missionary endeavors. The Briton Saint Patrick became the evangelist of Ireland during what he called his peregrinatio there, while Saint Samson left his home to ultimately become bishop in Brittany. The Irishmen Columba and Columbanus similarly founded highly important religious communities after leaving their homes.
Other Irish and British traditions 
A number of other distinctive traditions and practices existed (or are taken to have existed) in Britain or Ireland, but are not known to have been in use across the entire Celtic-speaking region. Different writers and commenters have identified different traditions as representative of Celtic Christianity.
A focus on monasticism – the sequestered life of monks and nuns – is often given as an example of Celtic Christian practice. Moreover, the claim is made that the true ecclesiastical power in the Celtic world lay in the hands of abbots of monasteries, rather than the bishops of dioceses. It is certain that the ideal of monasticism was universally esteemed in Celtic Christianity. This was especially true in Ireland and areas evangelized by Irish missionaries, where monasteries and their abbots came to be vested with a great deal of ecclesiastical and secular power. Following the growth of the monastic movement in the 6th century, abbots controlled not only individual monasteries, but also expansive estates and the secular communities that tended them. As monastics, abbots were not necessarily ordained (i.e. they were not necessarily priests or bishops). They were usually descended from one of the many Irish royal families, and the founding regulations of the abbey sometimes specified that the abbacy should if possible be kept within one family lineage.
This focus on the monastery has led some scholars, most notably Kathleen Hughes, to argue that the monastic system came to be the dominant ecclesiastical structure in the Irish church, essentially replacing the earlier episcopal structure of the type found in most of the rest of the Christian world. Hughes argued that the paruchia, or network of monasteries attached to an abbey, replaced the diocese as the chief administrative unit of the church, and the position of abbot largely replaced that of bishop in authority and prominence. According to this model, bishops were still needed, since certain sacramental functions were reserved only for the ordained, but they had little authority in the ecclesiastical structure.
However, more recent scholarship, particularly the work of Donnchadh Ó Corráin and Richard Sharpe, has offered a more nuanced view of the interrelationships between the monastic system and the traditional church structures. Sharpe argues that there is no evidence that the paruchia overrode the diocese, or that the abbot replaced the bishop; bishops still exercised ultimate spiritual authority and remained in charge of the diocesan clergy. But either way, the monastic ideal was regarded as the utmost expression of the Christian life.
The focus on powerful abbots and monasteries was limited to the Irish church, however; it was not universal across the Celtic world. The British church employed an episcopal structure corresponding closely to the model used elsewhere in the Christian world.
Irish monasticism was notable for its permeability. In permeable monasticism, people were able to move freely in and out of the monastic system at different points of life. Young boys and girls would enter the system to pursue Latin scholarship. Students would sometimes travel from faraway lands to enter the Irish monasteries. When these students became adults, they would leave the monastery to live out their lives. Eventually, these people would retire back to secure community provided by the monastery and stay until their death. However, some would stay within the monastery and become leaders. Since most of the clergy were Irish, native traditions were well-respected. Permeable monasticism popularized the use of vernacular and helped mesh the norms of secular and monastic element in Ireland, unlike other parts of Europe where monasteries were more isolated. Examples of these intertwining motifs can be seen in the hagiographies of St. Brigid and St. Columba.
This willingness to learn, and also to teach, was a hallmark of the “permeable monasticism” that so characterized the Irish monastery. While a hermitage was still the highest form of dedication, the monasteries were very open to allowing students and children within the walls for an education, without requiring them to become monks. These students were then allowed to leave and live within the community, and were welcomed back in their old age to retire in peace. This style of monasticism allowed for the monastery to connect with, and become a part of, the community at large. The availability of the monks to the people was instrumental in converting Ireland from paganism to Christianity, allowing a blend of the two cultures.
Rule of Columbanus 
The monasteries of the Irish missions, and many at home, adopted the Rule of Saint Columbanus, which was stricter than the Rule of Saint Benedict, the main alternative in the West. In particular there was more fasting and an emphasis on corporal punishment. For some generations monks trained by Irish missionaries continued to use the Rule and to found new monasteries using it, but most converted to the Benedictine Rule over the 8th and 9th centuries.
Again, however, the Rule of Columbanus was used exclusively in monasteries in the Irish sphere of influence; it was not followed in British monasteries.
Bede implies that in the time of Augustine of Canterbury, British churches used a baptismal rite that was in some way at variance with the Roman practice. According to Bede, the British Christians' failure to "complete" the sacrament of Baptism was one of the three specific issues with British practice that Augustine could not overlook. There is no indication as to how the baptism was "incomplete" according to the Roman custom. It may be that there was some difference in the confirmation rite, or that there was no confirmation at all. At any rate, it is unlikely to have caused as much discord as the Easter controversy or the tonsure, as no other source mentions it. As such there is no evidence that heterodox baptism figured into the practice of the Irish church.
Celtic Christian revivalism 
Ian Bradley notes that the recurrent interest in Celtic Christianity has led to successive revival movements he terms "Celtic Christian revivalism". According to Bradley, most, though not all, revivalists are non-Celts for whom Celtic Christianity has an "exotic and peripheral" appeal. Adherents typically claim their revivals restore authentic practices and traits of Celtic Christianity, though Bradley notes they actually reflect contemporary concerns and prejudices, and most are "at least partially inspired and driven by denominational and national rivalries, ecclesiastical and secular power politics, and an anti-Roman Catholic agenda." Though often inaccurate or distorted, the beliefs of these movements have greatly influenced popular conceptions of Celtic Christianity.
Bradley traces the origins of Celtic Christian revivalism to the Middle Ages. In the 8th and 9th century, authors wrote idealized hagiographies of earlier Celtic saints, whose "golden age" of extraordinary holiness contrasted with the perceived corruption of later times. Similarly, the 12th- and 13th-century literary revival popularized and romanticized older Celtic traditions such as the Arthurian legend. These ideas were expanded during the English Reformation, as Protestant authors appropriated the concept of a "Celtic Church" as a native, anti-Roman predecessor to their own movement.
In the 18th and 19th centuries, antiquarianism, the Romantic movement, and growing nationalism influenced ideas about what was becoming known as "Celtic Christianity". Beginning in the early 20th century, a full-fledged revival movement began, centered on the island of Iona and influenced by the Irish literary revival and more general Christian revivals. By the end of the 20th century, another wave of enthusiasm began, this time influenced by New Age ideals. Today, a self-identification with and use of "Celtic Christianity" is widespread in countries such as Ireland, both among participants in established churches and independent groups.
See also 
- Koch, p. 431.
- Koch, pp. 431–432.
- Corning, p. 18.
- Dáibhí Ó Cróinín, Early Medieval Ireland 400-1200 (London, 1995); T. M. Charles-Edwards, Early Christians Ireland (Cambridge, 2000); W. Davies, ‘The Myth of the Celtic Church’, in N. Edwards and A. Lane, The Early Church in Wales and the West (Oxbow Monograph 16, Oxford, 1992), pp. 12-21; Kathleen Hughes, ‘The Celtic Church: is this a valid concept?’, in Cambridge Medieval Celtic Studies 1 (1981), pp. 1-20; Kathleen Hughes, The Church in Early English Society (London, 1966); W. Davies and P. Wormald, The Celtic Church (Audio Learning Tapes, 1980).
- Peter Brown, The Rise of Western Christendom, 2nd edition (Oxford, Blackwell Publishing, 2003), pp. 16, 51, 129, 132.
- Patrick Wormald, ‘Bede and the ‘Church of the English’’, in The Times of Bede, ed. Stephen Baxter (Oxford: Blackwell Publishing, 2006), p. 207.
- Richard Sharpe, "Some problems concerning the organization of the Church in early medieval Ireland", Peritia 3 (1984), pp. 230-270; Patrick Wormald, "Bede and the 'Church of the English'", in The Times of Bede, ed. Stephen Baxter (Oxford: Blackwell Publishing, 2006), pp. 207-208, 220 n. 3
- Patrick Wormald, "Bede and the 'Church of the English’", in The Times of Bede, ed. Stephen Baxter (Oxford: Blackwell Publishing, 2006), pp. 223-224 n. 1
- Corning, p. xii.
- Bradley, p. vii–ix.
- Corning, p. 1.
- Koch, p. 432.
- Koch, p. 432–434.
- Corning, p. 4.
- Corning, p. 1; 4.
- Corning, p. 2.
- Corning, p. 2–3.
- Corning, p. 3.
- Hughes 2005, 310-311
- Lloyd, pp. 174–175.
- Lloyd, p. 180.
- Yorke, pp. 118–119
- Bede, Ecclesiastical History of England, London: George Bell and Sons, 1907; Bede says 1,200 British clergy died; the Anglo-Saxon Chronicle says 200. Bede is unclear on the date of the battle, but the current view is that it occurred in 616.
- Lloyd, pp. 175–177.
- Lloyd, p. 176 and note.
- Lloyd, p. 177.
- Tuchman, B. (1978) A Distant Mirror Ballantine Books, New York. ISBN 0-345-34957-1
- Hughes 2005, 306 & 310; Riley, 82-93, 95-96
- Ryan, 100-102
- Nordenfalk[page needed]; Pächt[page needed]
- Youngs, 15-16, 125
- Eric John, The Social and Political Problems of the Early English Church, in Anglo-Saxon History: Basic Readings, ed. David A. E. Pelteret (New York & London: Garland Publishing, 2000), p. 36.
- Eric John, ‘The Social and Political Problems of the Early English Church’, in Anglo-Saxon History: Basic Readings, ed. David A. E. Pelteret (New York & London: Garland Publishing, 2000), p. 37.
- Hughes 2005: 317
- Hughes 2005:, 313, 316, 319
- Hughes 2005: 319-320
- A. W. Haddan and W. Stubbs (ed.), Councils and Ecclesiastical Documents Relating to Great Britain and Ireland, 3 vols (Oxford, 1869-78), I, 112-3, Quoted in "The Catholic Encyclopedia".
- Corning, pp. 1–19.
- Patrick Wormald, Bede and the Church of the English, in The Times of Bede, ed. Stephen Baxter (Oxford, Blackwell Publishing, 2006), p. 224 n. 1.
- Eric John, The Social and Political Problems of the Early English Church, in Anglo-Saxon History: Basic Readings, ed. David A. E. Pelteret (New York & London: Garland Publishing, 2000), p. 34
- Ryan, p. 217.
- McCarthy, p. 146.
- McCarthy, p. 140.
- McCarthy, pp. 141–143.
- McCarthy, p. 141.
- A. W. Haddan and W. Stubbs (ed.), Councils and Ecclesiastical Documents Relating to Great Britain and Ireland, 3 vols (Oxford, 1869-78), I, 112-3
- McCarthy, Daniel (2003). "On the Shape of the Insular Tonsure". Celtica 24: 140–167. Retrieved June 18, 2009.
- McCarthy, pp. 147–148
- McCarthy, p. 149.
- McCarthy, pp. 142–143
- Medieval Handbooks of Penance, eds. John T. McNeil and Helena M. Gamer (New York, Columba University Press, 1938), p. 28
- Medieval Handbooks of Penance, eds. John T. McNeil and Helena M. Gamer (New York, Columba University Press, 1938), pp. 7-9
- Medieval Handbooks of Penance, eds. John T. McNeil and Helena M. Gamer (New York, Columba University Press, 1938), pp. 9-12.
- Medieval Handbooks of Penance, eds. John T. McNeil and Helena M. Gamer (New York, Columba University Press, 1938), pp. 13-17.
- Peter Brown, The Rise of Western Christendom, 2nd edition (Oxford: Blackwell Publishing, 2003), p. 252
- Corning, p. 17.
- This list includes information from Charles Plummer's essay, "Excursus on the Paschal Controversy and Tonsure" in his edition Venerablilis Baedae, Historiam Ecclesiasticam Gentis Anglorum, 1892 (Oxford: University Press, 1975), pp. 348-354.
- Koch, p. 433.
- Herren & Brown, p. 13.
- Hughes 2005, 311–312.
- Ó Cróinín, Dáibhí in Youngs, pp. 13-14
- Hughes 2005, 311 and note.
- Hughes 2005, 312.
- Eric John, ‘The Social and Political Problems of the Early English Church’, in Anglo-Saxon History: Basic Readings, ed. David A. E. Pelteret (New York & London: Garland Publishing, 2000), pp. 32-34.
- de Paor, Máire and Liam (1958). Early Christian Ireland: Ancient Peoples and Places. Frederick A. Praeger.
- de Paor, Máire and Liam (1958). Early Christian Ireland: Ancient Peoples and Places. Frederick A. Praeger.
- The main source for Columbanus's life or vita is recorded by Jonas of Bobbio, an Italian monk who entered the monastery in Bobbio in 618, three years after the saint's death; Jonas wrote the life c. 643. This author lived during the abbacy of Attala, Columbanus's immediate successor, and his informants had been companions of the saint. Mabillon in the second volume of his "Acta Sanctorum O.S.B." gives the life in full, together with an appendix on the miracles of the saint, written by an anonymous member of the Bobbio community.
- Lloyd, p. 175.
- Bradley, pp. viii–ix.
- Bradley, p. ix.
- Bradley, p. viii.
- Gierek, Bozena, "Celtic spirituality in contemporary Ireland". 300 - 317 in Olivia Cosgrove et al. (eds), Ireland's new religious movements. Cambridge Scholars, 2011
Primary sources 
- Adomnan, Life of Columba, ed. A. O. and M. O. Anderson, 2nd edition (Oxford Medieval Texts, 1991)
- Annales Cambriae, ed. Rev. John Williams ab Ithel (London : Longman, Green, Longman and Roberts, 1860)
- Bede, Historia Ecclesiastica Gentis Angelorum, in Venerabilis Baedae Opera Historica, ed. C. Plummer (Oxford, 1896)
- Cummian, De controversia paschali and De ratione conputandi, eds. Maura Walsh and Dáibhí Ó Cróinín (Toronto: Pontifical Institute of Mediaeval Studies, 1988), pp. 93–5.
- Gildas, De Excidio Brittaniae, ed. J. A. Giles, Six Old English Chronicles (London, 1848)
- Historia Brittonum, ed. J. A. Giles, Six Old English Chronicles (London, 1848)
- Medieval Handbooks of Penance, eds. J. T. McNeill and H. M. Gamer (New York: Columba University Press, 1939)
- Patrick (Saint), Confessio, ed. and trans. John Skinner (Image, 1998)
- Baring-Gould, S. (Sabine), The Lives of the British Saints,(1907) scanned by Google (alphabetized)
Secondary sources 
- Bradley, Ian (1999). Celtic Christianity: Making Myths and Chasing Dreams. Edinburgh University Press. ISBN 0748610472. Retrieved May 9, 2013.
- Brown, Peter. The Rise of Western Christendom: Triumph and Diversity, 2nd ed. (Oxford: Blackwell Publishing, 2003).
- Cahill, Thomas. How the Irish Saved Civilization (Anchor, 1996). ISBN 0-385-41849-3
- Charles-Edwards. T. M. Early Christian Ireland (Cambridge, 2000).
- Corning, Caitlin (2006). The Celtic and Roman Traditions: Conflict and Consensus in the Early Medieval Church. Macmillan. ISBN 1-4039-7299-0.
- Cróinín, Dáibhí Ó. Early Medieval Ireland: 400-1200 (London, 1995).
- Davies, Wendy. "The Myth of the Celtic Church", in The Early Church in Wales and the West, Oxbow Monograph, no. 16, edited by Nancy Edwards and Alan Lane, 12-21. (Oxford: Oxbow, 1992).
- Herren, Michael W.; Brown, Shirley Ann (2002). Christ in Celtic Christianity. Boydell Press. ISBN 0-85115-889-7.
- Hughes, Kathleen (1981). "The Celtic Church: Is This a Valid Concept? O'Donnell lectures in Celtic Studies, University of Oxford 1975". Cambridge Medieval Celtic Studies 1. pp. 1–20.
- Hughes, Kathleen (1966). The Church in Early Irish Society. London. ISBN 1-59740-067-X.
- Hughes, Kathleen (2005). "The Church in Early Irish Society: 400–800". In Ó Cróinín, Dáibhí. A New History of Ireland: Prehistoric and Early Ireland. Oxford University Press. ISBN 978-0-19-922665-8. Google Books link 2
- Koch, John T. (2006). Celtic Culture: A Historical Encyclopedia. ABC-CLIO.
- Lloyd, John Edward (1912). A History of Wales from the Earliest Times to the Edwardian Conquest. Longmans, Green, and Co. Retrieved May 17, 2010.
- McCarthy, Daniel (2003). "On the Shape of the Insular Tonsure". Celtica 24: 140–167. Retrieved June 18, 2009.
- Nordenfalk, Carl. Celtic and Anglo-Saxon Painting: Book illumination in the British Isles 600–800. New York: George Braziller, 1977.
- Pächt, Otto. Book Illumination in the Middle Ages (trans fr German), 1986, Harvey Miller Publishers, London, ISBN 0-19-921060-8
- Ryan, John. Irish Monasticism, Origins and Early Development, Talbot Press, Dublin, 1931
- Sharpe, Richard. ‘Some problems concerning the organization of the Church in early medieval Ireland’, Peritia 3 (1984).
- Wormald, Patrick. The Times of Bede: Studies in Early English Christian Society and its Historian, ed. Stephen Baxter (Oxford: Blackwell Publishing, 2006).
- Yorke, Barbara (2006). The Conversion of Britain: Religion, Politics and Society in Britain c. 600–800. London: Pearson/Longman. ISBN 0-582-77292-3.
- Youngs, Susan, ed. (1989). 'The Work of Angels', Masterpieces of Celtic Metalwork, 6th–9th centuries AD. London: British Museum Press. ISBN 0-7141-0554-6.
Further reading 
- Cahill, Thomas (1996). How the Irish Saved Civilization. Anchor Books. ISBN 0-385-41849-3.
- Corning, Caitlin (2006). The Celtic and Roman Traditions: Conflict and Consensus in the Early Medieval Church. Palgrave Macmillan. ISBN 1-4039-7299-0.
- Mayr-Harting, Henry. The Coming of Christianity to Anglo-Saxon England, 3rd edition (London: B. T. Batsford Ltd, 1991).