The British Isles of the sixth century are, in many ways, an undiscovered country. In fact, a paucity of surviving primary sources make the period largely undiscoverable, even though it is nestled between the fall of Rome and the rise of the Christian Church, both of which relied heavily on writing as an apparatus of government.

This is unfortunate, as it was a momentous century, full of change and drama. After the withdrawal of Roman troops from Britannia in 409/410, the British Isles underwent a period of seismic transformation. It was the “Age of Migrations” or, in modern parlance, “The Dark Ages.” All across Europe, entire peoples were on the move, amongst them, the Visigoths into Spain, the Vandals into North Africa, and the Lombards into Italy.

For its part, Britain saw the arrival of the Angles, the Saxons, the Jutes, and the Frisians. But it was crowded ground as these isles were already home to five peoples, each with its own customs, legal and political systems, myths of origin, gods, and tongues. And, rather than co-exist peacefully, the sources that we do have speak loudly of incessant internecine warfare as each sought pre-eminence over the other.

Britons, spreading across the whole of Britain up to and just over Hadrian’s Wall, held the lion’s share of the island at this time. As co-rulers with and the inheritors of Rome, they were in many cases already Christian, although polytheism and competing forms of Christianity continued apace well into the next century. They spoke an early form of Old Welsh and had taken up Latin as needed for the Church.

North of the Britons, in modern Scotland, were the Picts. They were also polytheistic and are likely to have spoken a form of Celtic, though whether it was P-Celtic (akin to Welsh, Cornish, and Breton), or Q-Celtic (akin to Irish, Manx, and Scots Gaelic) is still open to debate. Up until very recently, little had been known about the Picts, but a series of thrilling archaeological digs based out of the University of Aberdeen at enigmatic Pictish sites are finally bringing their culture to light, and it was far more advanced than previously understood.

In Ireland, the Irish were early and enthusiastic adopters of Christianity though, as in Britain, polytheism seems to have remained strong on the ground and through all levels of society. Their language was evolving into Old Irish at this time. And, in response to the Latin they saw being used in the Church, they quickly created their own written, runic language, called ogham, to capture their highly-developed and sophisticated oral culture and law codes, before also taking on Latin in earnest.

Finally, across the sea from them, in modern Argyll and the Isles, we find the Scots of the kingdom of Dalriada. Consummate seafarers, their language in the sixth century seems to have been interchangeable with the Primitive or Archaic Irish being spoken in Ireland, before evolving into the Scots Gaelic we have today. Although the Scots’ origin myths claim a foundation in about 500 by a certain Fergus Mór mac Eirc, a warlord from Antrim in Northern Ireland, we should instead view the peoples living on the shores of the North Channel as a single maritime culture with that body of water a highway linking them rather than a barrier. Indeed, before General Wade’s road-building programme in Scotland in the eighteenth century, a response to the threat of Jacobite unrest, it was easier to get around Scotland by boat. This was also true of Antrim, where the only access to many of the glens was by sea until, again in response to rebellion (that of 1798), the Antrim coast road was constructed in 1832-42. The local geographies, which today we find so picturesque, forced these people to look at one other, rather than back towards the rest of Ireland or Scotland. Indeed, on the ground, their material cultures appear indistinguishable.

This co-mingled history was highlighted quite spectacularly in a recent ground-breaking genetic study, the People of the British Isles (Nature, 19/3/2015). Among the 17 different genetic clusters identified in Britain and Northern Ireland were two which linked the North of Ireland to the Scottish lowlands and the Scottish highlands, suggesting to the geneticists an association with the kingdoms of Dalriada and Pictland respectively, perhaps as they emerged into written history in the years around 600.

Into this febrile mix came the Saxons, moving into the eastern shores of Britain where they displaced, enslaved, or intermarried with the Britons they encountered there. The Saxons, as we know, were to emerge the victors of the race to become the dominant political, cultural, and linguistic force in Britain, a pre-eminence which continues to this day. But while hindsight might encourage us to believe that this was inevitable, to the denizens of these isles in the sixth century the outcome was decidedly less sure. It was in many ways a free-for-all, the wild west, and perhaps nowhere more so than in Dalriada, which had the Picts to its north, the Irish to its west, the Britons to its south, and the Saxons moving into its east.

It is at this hinge point that my series, The Chronicles of Iona, is set. In it, I use one of Ireland and Scotland’s premier saints, Columba, or Colum Cille, of Iona, and Dalriada’s most successful warlord, Áedán mac Gabráin, as a dual lens through which to view this most pivotal period.

Columba, a Donegal prince and abbot, went on from exile to found the great monastery of Iona, a tiny island off the west coast of Mull with an outsized importance in the history of Europe. And under Áedán’s leadership, the kingdom of Dalriada, centred on the hillfort of Dunadd in Kilmartin Glen, grew from obscurity to its greatest territorial extent, forming the heart of the later mediaeval Scottish nation.

These are remarkable achievements, especially considering that Columba, who was born in about 520, and Aedan, born in about 534, also had the unlucky distinction of having lived through what a global community of scientists has recently described as “one of the worst periods to be alive”, with the year 536 designated “the worst year.” In that year, a cataclysmic volcanic eruption in Iceland plunged the Northern Hemisphere into a solid darkness, day and night, that lasted for 18 months. Two more eruptions followed in 540 and 547. These eruptions triggered a century of famine, cold weather, extreme drought, disease, and death. Communities unravelled and social norms were abandoned. It has been called “the worst global disaster in history.”

Yet, worse was to follow. The 570s, the setting for my new book, Cradle of Saints, the fourth in the series, witnessed the return to the British Isles of the “Plague of Justinian”—bubonic plague. Arising in Egypt in 541, by 543/4 the plague had spread to Britain and Ireland where it killed 35%-50% of the population. It remained active in Europe for two centuries. In 576, it was back, the Irish Annals making ominous note of plague and leprosy.

The economic stagnation and deprivation brought about by these dual natural catastrophes did not abate until about 640. It was a difficult time which, with its strident notes of climate crisis, large-scale migration, and pandemic, echoes our own. Yet, it was from this turbulent crucible that the seeds of the great Scottish nation were to sprout, and from which, thanks to the work begun on Iona at this time, learning, lost to the chaos of the age, was spread back to Europe and beyond.

Paula de Fougerolles is a medieval historian and author of The Chronicles of Iona.