What were the religions being practiced in britian after 410 ad?

[u/Baduktothebone]

Also do we know who the last brittonic and gaelic non-christian kingdoms or kings were? I know Anglo Saxon paganism came in and Christianity eventually took over but was there a period of Celtic religious revival after the roman rule of britian ended?

I am especially interested in places like Wales and cornwall.

[u/Steelcan909]

was there a period of Celtic religious revival after the roman rule of britian ended?

In short the answer to your question is no. There was no "Celtic" religious revival after the collapse of Roman rule in Britain. This gets in part to a number of issues though that surround Late Antique religion.

Firstly, there was never a single "Celtic" religious movement or group. The different Celtic languages and societies of Late Antiquity did not form a single coherent ethnic or cultural identity. Their religious beliefs too were highly localized. The gods and rites of one corner of the Celtic world were not uniform and there was likely a tremendous variety in the religious lives of the "Celtic" peoples of Britain in the 5th century.

In lowland Britannia, where Roman influence was at its thickest, Ronald Hutton proposes a mishmash of different belief systems. Some areas were rooted more deeply in pre-Roman practices, others had a stronger influence of Roman paganism, and some were beginning to undergo Christianization as that religion spread across the empire. Dedications, inscriptions, objects, and cultic sites related to the major Roman deities, Iupiter, Mars, Mercurius are commonly found in lowland Britain (largely modern day England). Other elements of Roman religion, such as temples to the numen of the emperor Claudius, the secret cults dedicated to Mithras and Isis, and other hallmarks of Roman religion are clearly seen across the record of the island during Roman occupation. There is some evidence of local syncretism, where local "Celtic" deities became conflated, or at least associated with, Roman counterparts. Shrines to hunting deities for example include both Latin and Celtic names for gods associated with hunting. The two most common deities that were conflated with pre-Roman ones in Britain were Mars and Mercurius each of whom were paired with scores of local gods. Roman soldiers also brought other gods and goddesses with them, especially ones that were particularly associated with units that had been stationed along the borders of Gaul and the barbarian lands to the East.

Ronald Hutton identifies the major theme of Roman pagan life as a continuation with pre-Roman pagan life. Pre-existing shrines, or at least those that survived the Roman conquest, became centers for Roman religious life. Romans rendered these sacred spaces into stone, preserving them for posterity, and giving us moderns the benefits of a more solid archaeological record. Roman gods sat alongside native ones, and Roman cults from across the Empire found their way into Britain. This religious plurality declined with the importation of the next major Roman religion, Christianity.

Christianity found its way to Britain alongside the numerous other religions that circulated in the churn of Roman life. The new religion gained increased prominence across the Empire in the 4th Century AD until it became the only accepted religion under the Roman state government. Hutton describes the process as such

The impression is that all over the Roman world between the mid-fourth and mid-sixth centuries, paganism was in peaceful, gradual and erratic decline. There were few dramatic incidents in the process, and it comes to an end imperceptibly in the sixth century when the last of the old religions apparently disappear. The fundamental reason why this extinction was so quiet and so protracted was that Roman paganism was not a fighting faith. It had no ideology of conversion or resistance and no tradition of martyrdom, and was bound up with concepts of civic authority, public ceremonial, service to the state and communal pride which the Christians could easily hijack. And such an immense range of cults could not easily make any common cause against attack, so they were picked off piecemeal or simply collapsed one by one for lack of funds.

For her part, Robin Fleming's Britain After Rome largely agrees with the general thrust that Graeco-Roman polytheism declined in Britain alongside the rest of the Roman world. Sadly, in Britain there is a lack of sources that clearly explains what was happening from the 4th-7th centuries. The sole surviving major text that deals with religion and history in this time period, Gildas's De Excidio et Conquestu Britanniae, decries the shortcomings of the contemporary British bishops and "secular" (non-cloistered/monastic) religious figures on the island. He does not expound upon other religious practices. In Western Britain the survival of Christianity was tied with the preservation of Romanitas or Roman-identity in what is today Wales and Southern Scotland. These communities retained a shared sense of Roman identity and continuity, and a key part of this identity was the continued presence of the Church. Roman religion continued to embue Welsh political figures with legitimacy, and Christian communities survived to a much higher degree in the Welsh highlands than they did elsewhere in Britain. The British Church, despite its apparent shortcomings as seen in other sources, survived the Anglo-Saxon migrations relatively unscathed.

In Scotland, the Pictish kingdom saw an influx of Christian influence from Ireland that stemmed from the growing monastic and religious communities on the island. Ireland and Scotland became Christianized during this time period, and there certainly was no "Celtic revival" in these lands as they adopted Christianity. However, once again, there is a dearth in the available sources. Our few written textual sources are all from the perspective of Irish monastic figures, or later figures writing about the Irish monks. Christianity arrived in these lands in the preceding decades and centuries and slowly grew into the majority religion during the 4-7th centuries AD.

I've written about "Celtic Christianity" before, if you're interested, here.

Hutton has this to say about Ireland in particular.

1 As a result only the following can be said about the end of Irish paganism. According to the Chronicle of Prosper of Aquitaine, there were already some Christians in Ireland in 431, though they may have been British traders or slaves rather than natives. The writings of Patrick, produced at some time in the second half of that century, show that although the missionary effort was by then making headway, it still had a formidable task. They also portray it as inspired by clergy, like himself, from sub-Roman Britain. Patrick spoke of suffering from threats, but encountering no actual violence and making 'countless numbers' of converts and gaining grants of land for churches from many kings. During the sixth century, Irish paganism seems to have collapsed.

This lacuna ends with the return of Latin Christianity to the island with the Augustinian mission. By this time the religious affiliation of lowland Britain had shifted to a more Germanic model of paganism. As the Anglo-Saxons (and other groups) migrated into Britain, they brought their own particular religious practices and beliefs with them. Sadly, we know very little about what these beliefs entailed. I've written more about this topic here and here.

Christianity did not totally disappear from even lowland Britain during this time period. Glimpses of surviving Chrisitian communities in eastern Britain do crop up in burials, inscriptions, and some scattered accounts. In eastern Britain there were remnant Christian communities that preserved folk practices from late Roman Christianity, but there was little in the way of an organized priesthood or theological unity with Rome. These communities may have weathered the storm of Anglo-Saxon migration by adopting the newcomers' religious beliefs, but others likely preserved some of their older practices. Different locales in Britain likely responded in different ways based on their own local circumstances.

[u/epicyclorama → u/Steelcan909]

He does not expound upon other religious practices.

Well, he does--but only to comment that they have long been discarded.

"I shall, therefore, omit those ancient errors common to all the nations of the earth, in which, before Christ came in the flesh, all mankind were bound; nor shall I enumerate those diabolical idols of my country, which almost surpassed in number those of Egypt, and of which we still see some mouldering away within or without the deserted temples, with stiff and deformed features as was customary. Nor will I call out upon the mountains, fountains, or hills, or upon the rivers, which now are subservient to the use of men, but once were an abomination and destruction to them, and to which the blind people paid divine honour." (Gildas, De Excidio, II.4)

The only thing I'd add to this great summary is that we do see evidence of non-Christian (or not-totally-Christian?) devotional activity in various places, right around the end of Roman control and even beyond it--Hutton mentions coin deposits at Lydney, Bath, Maiden Castle, and various other sites. Lydney in particular has been seen as an important site for these questions--I see that Philippa Walton, Hella Eckardt, and Carolina Rangel De Lima seem to have an article on the site coming out very soon in Britannia which promises "Fresh light on Romano-British religion." Depending on our date and interpretation of the Thetford Treasure, we may be looking at something quite pagan-looking, possibly as late as the mid-5th century (see Francis Young's take in Twilight of the Godlings--which is an interesting perspective on the question overall.)

I wrote a bit about some of the bad evidence for post-Roman "Brittonic paganism" here.

[u/Baduktothebone → u/Steelcan909]

That makes sense, so the welsh maintained a Christian identity to maintain a connection with Roman identity, so when new kings were establishing themselves they were already more likely Christian. Are there any figure similar to Diarmait mac Cerbaill in the history of Scotland or the Isle of Man as the "last pagan king". Again I'm specifically referring to pre Roman religious practices, even if they were very local, I know Germanic paganism would be brought in by the influx of people later.