East Carmarthenshire is particularly interesting if by paganism we mean not only organised modern Pagan religion, but the much older relationship between landscape, sacred places, supernatural beings, wells, trees, mountains and seasonal practice.

There are really three layers to distinguish.

Pre-Christian religion. The archaeological landscape around Llandeilo, Dinefwr, Carreg Cennen and the Black Mountain shows very long occupation. Dinefwr contains an Iron Age hillfort predating the Roman forts there, while Carreg Cennen has evidence of prehistoric occupation and human remains. Intriguingly, Llandyfeisant church at Dinefwr is traditionally thought to stand on the foundations of a Roman temple. We cannot safely identify particular Celtic gods with these sites, however; the archaeological evidence is much stronger for ritual landscapes than for named deities.

Carreg Cennen is especially fascinating. The natural cave beneath the castle contained human remains and a perforated horse tooth, perhaps worn as a bead or pendant. Modern radiocarbon work dated the tooth to the later Roman–early medieval period. That doesn't prove pagan worship, but it demonstrates that the cave continued to have human significance across the period when Christianity was becoming established.

The Christianisation of an older sacred landscape may actually be the most interesting aspect of East Carmarthenshire. Llandeilo became an extremely important early Christian centre associated with St Teilo; by the ninth century its religious community was one of the most important in Wales. But conversion did not necessarily mean that people's older understanding of a living or spiritually inhabited landscape disappeared. Wells became saints' wells; significant trees acquired Christian associations; supernatural beings survived as fairies, spirits and legendary characters; and older seasonal customs could acquire Christian interpretations.

This is where I think there is a particularly interesting connection with your interest in spiritual governance and Rights of Nature. The Carmarthenshire evidence doesn't necessarily point to a neat institutional "Celtic pagan religion". It points towards something closer to a relational ontology of landscape: particular waters, woods, caves, hills and animals possessing significance beyond their usefulness as resources.

The Black Mountain/Mynydd Du–Amman Valley–Llandeilo landscape would therefore be a very fruitful area to investigate. The limestone and sandstone geology around Carreg Cennen produces a mosaic of ancient woodland, marshy grassland, wet heath, springs and rivers; both the Cennen and Loughor arise in this landscape. Such conspicuous natural features are precisely the kinds of places around which Welsh folklore accumulated.

And then there is medieval Welsh mythology. We have to be careful here. The Mabinogion and related material were written down in a Christian society, so characters such as Rhiannon, Arawn, Bran, Gwydion and others cannot simply be labelled "the pagan gods of Wales." Nevertheless, many scholars regard elements of these stories as preserving substantially older mythological traditions. The distinction between human society, animals, landscape and the Otherworld is strikingly permeable.

That makes Carmarthenshire particularly significant because Carmarthen itself and the surrounding landscape became associated with Myrddin/Merlin, while the Black Book of Carmarthen preserves some of the earliest Welsh material concerning Myrddin and other legendary traditions. The "Battle of the Trees" (Cad Goddeu) is not actually in the Black Book—an important distinction—but belongs to the Book of Taliesin tradition.

Finally there is modern Paganism. There are Druids, Wiccans, Celtic reconstructionists, animists, witches and more loosely defined nature-spiritual practitioners across Wales, including southwest Wales. But modern Welsh Paganism shouldn't automatically be treated as an uninterrupted survival of Iron Age religion. Much of modern Druidry, for example, was profoundly influenced by the eighteenth-century revival and Iolo Morganwg. Contemporary practitioners themselves often recognise that distinction.

For East Carmarthenshire specifically, I think a more interesting question than simply "Were there pagans here?" would be:

To what extent does East Carmarthenshire preserve evidence of a pre-Christian or non-Christian ontology in which particular elements of the natural world possessed agency, personhood or sacred status?

That could take us into holy wells, sacred trees, caves, standing stones, prehistoric monuments, fairy places, Myrddin traditions, place-names and local folklore from the Amman Valley, Llandeilo, Llandybie, Carreg Cennen and Mynydd Du.