Fairy Forts & the Hidden Souterrains Beneath Them
Those grassy rings no farmer will plough through are 1,500-year-old ringforts, and many hide a secret souterrain underground. Here's what they are, and the folklore that kept them safe.
Drive almost anywhere in the Irish countryside and, sooner or later, you'll spot one: a low, circular bank of grass in the middle of a field, often crowned with a scraggly hawthorn tree, that the farmer has quietly ploughed around rather than through. That's a fairy fort, and there are tens of thousands of them.
They are one of the most common ancient monuments in Europe, and many hide a secret directly beneath your feet.
What a "fairy fort" really is
The fairy fort is the folk name for a ringfort: in Irish a ráth (the bank) or lios (the enclosure inside it). Around 40,000 once dotted the island, and roughly 32,000 are still visible today. Despite the dramatic name, most were not military forts at all but enclosed family farmsteads, built and lived in mainly between about 500 and 1000 AD. A circular earthen bank and outer ditch, sometimes topped with a timber palisade, ringed a yard with a thatched roundhouse, keeping the cattle in and wolves and raiders out.
The secret underground: souterrains
Here's the part most people never learn. Beneath many ringforts lies a souterrain (from the French for "under-ground"; uaimh, "cave", in Irish), a hidden network of stone-lined passages and chambers dug into the earth. About 3,500 are known, concentrated in the north and west.
They were astonishingly clever. Entrances were camouflaged, often inside the house itself. Passages were built low and narrow, with a deliberate squeeze called a "creep-way", sharp turns and sudden drops, so an intruder had to crawl in one at a time and could easily be stopped by a single defender. And they served two jobs at once:
- a cool, dry store for milk, butter and meat, an early-medieval fridge;
- a hiding place when a Viking or rival war-band came raiding, complete with an air vent so a family could shelter below for hours while the fort was ransacked above.
Where the fairies come in
So why "fairy" forts? Long after the farmers were gone, people looked at these grassy rings, with dark, hollow passages running underground, and believed they were the homes of the Aos Sí, the fairy folk: the old gods who, in the myths, had withdrawn beneath the hills after their defeat. The real souterrains almost certainly fed the belief. Here were actual tunnels leading down into the earth, into the Otherworld.
To disturb a fairy fort was to invite ruin. You did not plough it, build on it, or cut the lone sceach gheal (whitethorn "fairy tree") growing on it. The stories of those who ignored the warning, of bad luck, illness and worse, are still told.
Superstition as a conservation law
And here's the lovely twist: that fear saved history. Because generation after generation of farmers left the forts untouched, an enormous amount of Ireland's early archaeology survived where it would otherwise have been flattened: the ringforts and the souterrains beneath them. It's no dusty old belief, either: as recently as 1999 the folklorist Eddie Lenihan helped reroute a County Clare bypass to spare a single fairy bush. All over Ireland there are still fields with a stubborn green ring in the middle that no one will touch.
See it for yourself
We've built an interactive diagram so you can explore one. Flip between a cutaway, a ground-level side view and an aerial plan, then tap any part (the bank, the ditch, the house, the hidden souterrain entrance, the creep-way, the chamber, the air vent) to learn what it was and hear its Irish name spoken.
👉 Explore the Fairy Forts & Souterrains page
Ná cuir isteach ar an lios. Don't disturb the fairy fort. 🍀