It is a theory more than 15 millennia in the making, and it carries the air of an archaeological thriller. Researchers now believe the earliest known people to walk Ireland’s soil almost certainly came not by boat but on foot — across a vanished land bridge from what is today Pembrokeshire.
A team led by Dr George Nash, a rock-art specialist at Liverpool University, has uncovered eight cave sites in south-west Ireland bearing engravings, ochre paintings and finger-grooved sketches dated to at least 15,000 years ago — roughly 5,000 years before any previously documented evidence of human habitation on the island.
The find, the fruit of a multi-year collaboration called the Lost Land Bridge Project, redraws the earliest chapter of Ireland’s human story and reframes Wales not merely as a Celtic heartland but as a launching pad for one of Europe’s last great prehistoric migrations.
A frozen highway across the Irish Sea
During the last glacial maximum, conditions were brutal. Summertime temperatures hovered between minus 10°C and minus 20°C, and an ice sheet smothered much of the British Isles. Yet sea levels were roughly 120 metres lower than today, exposing a forested, grassy land corridor that stretched around 76 kilometres (46 miles) coast to coast between south-east Wales and the Rosslare area.
This strip of habitable terrain would have teemed with wild horses, mammoth, bison and reindeer feeding on sedges, mosses and lichens clinging to the permafrost soil. For ice-age hunter-gatherers, it was an irresistible highway west.
Nash said he had long considered it “inconceivable” that early humans would not have used the crossing. “Up until now the earliest evidence archaeologists had found — through accidental discovery — was from around 10,500 years ago, but everyone — not just me — knew that simply couldn’t have been correct,” he said.
How AI helped narrow the hunt
The breakthrough came not from a single eureka moment in a damp Irish cave but from a laptop. Working with caving specialist Shane Diffily and digital mapping consultant Darren Lee, the team fed an algorithm with every known characteristic of prehistoric cave dwellings in south Wales — from entrance orientation to geological composition.
The model flagged 28 candidate sites across south-west Ireland. Eight have so far yielded rock art.
“It’s all very exciting,” Nash said. “The principle we worked on was ‘absence of proof isn’t proof of absence’.”
He is blunt about what changed: AI was, in his words, “a game-changer”, sparing the researchers years of fruitless tramping through the Irish countryside and channelling their efforts to where the geology most resembled the south Welsh sites.
From primitive lines to figurative art
The cave art itself tells a story of cultural transmission across what was, even then, a frontier. The earliest surviving works from the Gower Peninsula — simple lines gouged into soft limestone — may have functioned as tally charts or early symbolic marks.
Over some 20,000 years, that visual language evolved into the figurative engravings and ochre paintings Nash’s team has now documented in Ireland, including depictions of a mammoth and a cervid deer. The most tentative images, gouged by three or four fingers into clay walls, were probably the work of children being initiated into the practice of rock art.
Nash said competition for cave space would have been ferocious. There were roughly 100 human-occupied caves on Gower alone, and the ambient temperature inside — a steady 10°C to 15°C year-round — made them, with a fire at the mouth and a bearskin across the entrance, “quite a cosy place to live, especially compared with the minus 20°C outside”.
As family networks expanded and knowledge of animal migration patterns sharpened, pressure to push further west and north would have mounted.
What comes next
The team is keeping the precise locations of the caves under wraps to protect them from vandalism and looting, but Nash is convinced there is much more to find. “The sites we’ve currently explored are in south-west Ireland, but it’s illogical to presume that early humans just bypassed Wexford, Waterford and Cork, and ploughed on west,” he said. “There must be more, and even earlier places which are just waiting for us to find them.”
The Lost Land Bridge Project draws on expertise from University College Dublin, the University of Adelaide, and academics in Dubai, Wales and Portugal — a deliberately wide net for a question that sits at the intersection of climate science, archaeology and human migration.
It also raises a tantalising possibility: if Welsh humans reached Ireland 15,000 years ago, the genetic and cultural threads tying the two nations may stretch back far further than any historian has dared to claim.
Why it Matters
This discovery rewrites the opening chapter of Irish prehistory and repositions Wales as the cradle of Britain’s earliest westward migration — a migration made possible by a lost landscape now lying beneath the Irish Sea. Beyond the academic rewrite, it showcases how machine-learning tools are reshaping fieldwork in disciplines long defined by trowel and torchlight, pointing the way to a generation of discoveries that may soon redraw the prehistoric map of north-west Europe.