Here Be Dragons: 5 Kaiju-Sized Monsters From Irish Mythology

Norse mythology has a giant wolf, Fenrir; and a “world serpent,” Jörmungandr; and Surtr, a mountain-sized jötunn with a skyscraper-sized flaming sword.

Indian mythology has the Rakshasas, man-eating demi-gods with tiger-like fangs and claws who can change size at will.

Chinese mythology boasts the nearly 33-foot-tall Fangfeng, who has the head of a dragon and the ears of an ox.

Greek mythology has the Titans, of course, those massive, pre-Olympian deities, as well as their descendants, among them Cerberus, the multi-headed hound of Hades, and the Hydra, the multi-headed serpentine water monster that was famously bested by Heracles (a.k.a. Hercules) as part of his Twelve Labors.

Surely, Irish mythology—a collection of stories known for its abundance of “superpowered” hero-gods wielding magical weapons in mystical lands—would see said hero-gods face-off against some super-sized villains.

And yet…

When you think about Irish mythology’s biggest, baddest monsters, who do you think of?

Balor of the Evil Eye, no doubt. He is a monstrous, cunning corsair, to be sure—but Balor is not the lumbering, building-sized monster we’re so accustomed to seeing in medieval fantasy films, a monster that gets taken out either A) in the opening scenes (think the dragon in Thor: Ragnarok) as a way of establishing a hero’s prowess; or B) in the third act, like with the Kraken in Clash of the Titans (the original, 1981 version, of course). 

The reality is, Irish myths and legends are more well-known for their mischievous and sometimes murderous humanoid monsters and (roughly) human-sized shapeshifters: the banshee, wolfwalkers, Púcas, the Dullahan, Abhartach the vampire.

That being said, there is bigger fare to be found, if one knows where to look (hint: at the bottom of lakes—more on that soon). And no, I don’t mean Irish giants, who, while monsters in their own right, tend to think and behave quite like normal human adversaries (they live in houses, go to parties, get married, etc.).

What I’m on the proverbial hunt for here are real, honest-to-goodness Irish dragons. Mythical dragons, obviously. You know what I mean. Fortunately, they shouldn’t be too hard to find. To quote historian Peter Berresford Ellis:

“Irish mythology abounds with monstrous serpents or dragons, most of whom live at the bottom of lakes. Sometimes they guard palaces or fortresses. However, there have never been any venomous reptiles in Ireland. There is a species of small lizard, called are-luachra or lizard of the rushes. Two centuries before St. Patrick was supposed to have driven out all the serpents, writers were stating that no such creatures existed in Ireland.”

source: A Dictionary of Irish Mythology (1987)

Yes, Ellis goes on a bit of a tangent pointing out that St. Patrick didn’t drive the snakes out of Ireland, but his initial point is clear enough:

Here—in the Ireland of myth and legend—be dragons.

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5 of the Most Dangerous Dragons From Irish Myth and Legend 

1. The Oilliphéist

Perhaps the closest thing Irish mythology has to a “proper” dragon (as viewed through a Western lens), the oilliphéist is a category of monster typified by its immense size and serpentine appearance.

Also known as the oillpheist, its name is comprised of the root words oille, meaning great or vast, and péist (also: pheist), meaning “fabulous beast,” “monster,” “reptile,” or “worm.” Worth noting: in some texts, péist is translated directly as “dragon”.

In W. B. Yeats’ 1888 work Fairy and Folk Tales of the Irish Peasantry, the famed Irish poet makes a fleeting reference to a “Lake-dragon” called the Payshtha. The name Payshtha, according to Yeats, is derived from the Old Irish word píast (Latin: bestia) which, wouldn’t you know it, is an alternate form of the word péist.

Indeed, Irish myths and legends are full of péists.

In the Táin Bó Fráech (Cattle Raid of Fráech), a story that dates back to at least the 8th century C.E., the warrior Fráech (a.k.a. Fraoch, Fraích, and Fróech) is forced to battle a péist after Ailill and Medb (a.k.a. Maeve), the king and queen of Connacht, trick him into taking a swim in a monster-infested lake. As Celtic and Irish studies professor James MacKillop explains:  

“Ailill, fearful that Fráech might elope with his daughter, steals the gift thumb ring and throws it into the water, where it is swallowed by a salmon. He also commands that Fráech fetch some rowan berries that will prolong life and cure illness. As Ailill knows, the berries are near the dwelling of a dragon [Ir. péist], which he hopes will devour the swain.”

source: A Dictionary of Celtic Mythology (1998).

Long story short: Fráech gets his hands on a sword and slays the dragon, “but is wounded in the venture.” Hundreds of fairy-women (“maidens from the sídh”) show up and carry him to the Celtic Otherworld to heal him. He then makes a triumphant return to Ailill’s palace at Cruachain (a.k.a. Cruachan).

Fun fact: Some scholars believe this story, the Táin Bó Fraích, was the main inspiration for the English Beowulf saga. But I digress…

Another péist—or rather, a trio of péists—can be found in The Story of Conn-eda, which also goes by the title The Golden Apples of Lough Erne. The story tells of a prince, Conn-eda, who, at the behest of a talking horse, follows a magic ball thingie into a lake. (Yeah, this story is kind of bonkers.)

Here, I’ll let Yeats tell it:

“When he entered the lake the ball again appeared, and rolled along until it came to the margin, across which was a causeway, guarded by three frightful serpents; the hissings of the monsters was heard at a great distance, while, on a nearer approach, their yawning mouths and formidable fangs were quite sufficient to terrify the stoutest heart. “Now,” said the horse, “open the basket and cast a piece of the meat you find in it into the mouth of each serpent; when you have done this, secure yourself in your seat in the best manner you can, so that we may make all due arrangements to pass those draoidheacht peists. If you cast the pieces of meat into the mouth of each peist unerringly, we shall pass them safely, otherwise we are lost.” Conn-eda flung the pieces of meat into the jaws of the serpents with unerring aim.”

source: Fairy and Folk Tales of the Irish Peasantry (1888)

FYI: The word draoidheacht translates literally to “druidic,” but can also mean “magical” or “enchanted.” Hence, the aforementioned “draoidheacht peists” are essentially enchanted dragons.

But what about the BIG dragons? The oilliphéists.

Perhaps the most famous oilliphéist comes from Irish folklore: Caoránach.

According to MacKillop, Caoránach (a.k.a. Coal) was “the monster banished to Lough Derg (Co. Donegal) by St Patrick. Perceived as female, she was said to be the mother of demons or devils.”

Interestingly, there is a second oilliphéist associated with St. Patrick. In a “late legend,” according to Ellis, an oilliphéist learns of St. Patrick’s plan to eradicate Ireland’s serpents and preemptively high-tails it to the Atlantic. To quote Ellis:

“The oillpheist fled toward the sea cutting its way through the land forming the River Shannon. On its way it swallowed a piper named Ó Ruairc [O’Rourke] who continued to play his pipes to the beast’s discomfiture so that it finally threw him back to land.”

Now that is a Kaiju-sized Irish monster.

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2. The Cata

Just when you thought it was safe to go into the River Shannon, a new monster appears: the Cata.

The Cata has been described as Ireland’s own Loch Ness Monster. According to legend, it dwells in the River Shannon, Ireland’s longest river, and sightings of the aquatic cryptid have been reported as recently as the 1960s.

(Apparently, the Cata’s favorite bathing spot is Lough Ree, one of three major lakes along the River Shannon, in case you were hoping to do some monster-hunting of your own.)

At first glance, the Cata seems like it could be a continuation of the oilliphéist/St. Patrick legend—i.e., maybe the monster that created the River Shannon never actually fled to the sea, but has instead been hiding out in the Shannon’s darkest depths for centuries.

Upon closer inspection, however, it becomes clear that the Cata is its own monster, one that doesn’t fit the profile of the aforementioned oilliphéist.

First described in the 15th-century Book of Lismore (a.k.a. the Book of Mac Carthaigh Riabhach), the Cata is known for “having a horse-like head with a mane, gleaming eyes, thick claws with nails of iron and a whale’s tail,” according to author M. G. Boutet (source: Celtic Astrology from the Druids to the Middle Ages, 2017). Boutet also notes that the name Cata is derived from the root word catta, meaning pugnacious.

Of course, another possibility is that the creature’s name is Cata because…it’s a big ole cat. The Irish word for cat is—wait for it—cat. And as Ellis explains, monster-cats in Irish mythology are not without precedent: 

“Cats permeate the myths, for example Irusan of Knowth who would often make off with people. Three monstrous cats dwelt in the Cave of Cruachan, the entrance to the Otherworld.”

source: A Dictionary of Irish Mythology (1987)

This feline interpretation of the Cata is recorded in the Life of St. Senan, the hagiography of a sixth-century, County Clare-born bishop who established an abbey on Inis Cathaigh (Scattery Island) in the Shannon Estuary. To quote Michael Mac Mahon’s Customs, Lore and Legend of Other Clare Days:

“Here the otherworld creature was a large cat (called the Foracat) who, amongst other things, devoured the saint’s smith, Narach, but Senan rescued him in the nick of time and brought him forth alive. The story is recorded in the Life of St. Senan which goes on to state that the monster was chained by the saint to the bottom of Doolough lake, near Mount Callan.”

However, in another version of the story—the one that evidently became more popular as the years went on—the cat-monster is swapped out for a creature more closely resembling a péist. Indeed, in Thomas Johnson Westropp’s A Folklore Survey of County Clare, the Cata is referred to as the “first in importance amongst the péists.”

The action beats in this version of the story remain largely the same: the Cata swallows St. Senan’s smith. Senan rescues him. They chain the monster and banish it to Doolough (the black lake) at the base of Mount Callan.

In between, however, we find this description of the Cata as it attacked: “‘its eyes flashing flame, with fiery breath, spitting venom and opening its horrible jaws,” (source: Prose Life of St. Senanus).

Now that’s definitely a dragon.

Then again…the flashing eyes and open jaws do make it sound a bit like a hissing monster-cat.

And remember that other big Irish cat, the one Ellis mentioned? Irusan of Knowth? Welp, according to legend, Irusan (also: Írusán) snatches up a famed poet by the name of Senchan (also: Senchán)—a name similar to Senan, perhaps suspiciously so.

What’s more, in the Irusan lore (as in Cata lore), a sixth-century Irish saint—this time St. Ciarán—saves the day, rescuing a victim from the jaws of the beast.

But we’re not done yet, because there is another “parallel” Irish monster we can hold up against Cata and Irusan, the brocshee or Brioch-Seach (fairy badger), which, according to legend, was defeated and chained up by yet another sixth-century Irish saint, St. Mac Creiche. The location this time: County Clare’s Lough Raha (Rath Lake).

The implication here isn’t that one of these stories is definitively “the original” and the others copied it (although that’s certainly plausible). Instead, the bigger takeaway here is that there is clearly a formula to these stories. An underlying blueprint. What Scottish folklorist J.F. Campbell calls The Celtic Dragon Myth.

The names and places and monsters may change, but the formula dictates certain events and character moments must happen. (Yes, just like in most films set in the Marvel Cinematic Universe. And I say that as a fan.)

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3. The Muirdris (a.k.a. Sinach)

Call it a water monster; call it a sea-monster; call it a sea-dragon; call it “a vast dragon-serpent,” to quote Martin Arnold’s Dragon: Fear and Power (2018).

And hey, if you are going to call the Muirdris “a vast dragon-serpent,” you might as well call it an oilliphéist, because as we learned in the first section, that’s what the word oilliphéist means: vast reptile.

But I digress.

To the best of my knowledge, the Muirdris—later known as the Sinach, Sineach, or Sinech—first appears in the 16th-century text Echtra Fergusa maic Léti (The Adventure of Fergus mac Léti). 

The text follows a mythical king of Ulster who (with the help of some magical shoes provided by the fairy king Iubdán, naturally) explores the depths of Dundrum Bay (a.k.a. Lough Rudraige / Loch Rury) in the County Down.

Upon viewing the monstrous Muirdris for the first time during one of his magical scuba sessions, Fergus’s face is left disfigured by the creature’s duiderc (death-gaze). The semi-aquatic king surfaces with his life, and with the knowledge that there’s only one way to cure his disfigurement:

He must return with his sword and magic fairy shoes and slay the Muirdris.

Here, I’ll let poet Sir Samuel Ferguson tell the rest:

For a day and night
Beneath the waves he rested out of sight,
But all the Ultonians on the bank who stood
Saw the loch boil and redden with his blood.
When next at sunrise skies grew also red
He rose—and in his hand the Muirdris’ head.
Gone was the blemish! On his goodly face
Each trait symmetric had resumed its place:
And they who saw him marked in all his mien
A king’s composure, ample and serene.
He smiled; he cast his trophy to the bank,
Said, ‘I, survivor, Ulstermen!’ and sank.

source: Myths & Legends of the Celtic Race (1911)

Now, in later iterations of the story, the Muirdris starts going by a new name, Sinach (also: Sineach, Sínach, and Sinech), which, according to MacKillop, means “stormy.”

Ellis, however, argues that “Sineach” means “having teats or paps,” thus implying that the monster in question is not some vast reptile, but a mammal.

For the record, the presence of mammalian features shouldn’t disqualify the Muirdris/Sínach from “dragon” status. After all, the Greek chimera—arguably one of the oldest dragons (or, perhaps more accurately, proto-dragons) known to European mythology—had the body of a goat and the head of a lion (paired with the tail of a serpent).

It’s also possible that the Muirdris/Sínach has an equine connection, and is perhaps more closely related to the Scottish kelpie—a shapeshifting water spirit that appears on land as a horse—than to your classic, scaly, fire-breathing dragon.

Indeed, author T. W. Rolleston describes the Muirdris as a “river-horse” in his 1911 work Myths and Legends of the Celtic Race.

“Fergus was never tired of exploring the depths of the lakes and rivers of Ireland; but one day, in Loch Rury, he met with a hideous monster, the Muirdris, or river-horse, which inhabited that lake, and from which he barely saved himself by flying to the shore.”

In this version, the Muirdris/Sínach isn’t a péist at all. Instead, the monster resembles what Yeats calls the Augh-iska, or “Waterhorse.”

The Irish Augh-iska has a Scottish counterpart in the each-uisge, which also means “water horse.” In fact, the word “Augh-iska” is merely an anglicization of the Gaelic each-uisge (Scottish Gaelic) or each-uisce (Irish). Etymology aside, this is one nasty beast—“perhaps the fiercest and most dangerous of all the water-horses,” according to folklorist Katharine Briggs (source: An Encyclopedia of Fairies, Hobgoblins, Brownies, Boogies, and Other Supernatural Creatures, 1976).

Unlike its cousin the kelpie, the each-uisge is more than just mischievous: it is a murderous, carnivorous opportunist who lures children onto its back by taking the form of a cute little pony. Upon reaching the water, the each-uisge’s skin becomes sticky. The children can’t get off. The each-uisge drags its victims to the deepest part of its hunting ground, drowns them, and eats their bodies wholesale. 

Oh, except for their livers, according to Briggs. Those float to the surface.

Lovely.

Needless to say, even in its water-horse incarnation, the Muirdris/Sínach is clearly not an Irish monster you’d want to mess with.

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4. Ellén Trechend

Finally, a three-headed dragon.

You really can’t make a list of dragons without including at least one King Ghidorah-esque, three-headed dragon. It’s an unwritten rule.

And when you do a Google image search for “Ellén Trechend,” what comes up? Bingo. Beautiful paintings and other illustrations of a scaly, snarling, building-sized monster with massive, leathery wings and three serpentine heads. 

Ellis describes Ellén Trechend simply yet unambiguously as “a three-headed monster which came out of the cave of Cruachan.”

But did you catch that last bit? Cruachan.

This is now the third time we’ve heard about it.

The first: Ailill’s palace, as mentioned in the Táin Bó Fraích, is located at Cruachan (a.k.a. Cruachain), which was the capital of the ancient Irish kingdom of Connachta.

The second: the trio of monster-cats, mentioned in passing while discussing the Cata’s origin, lived in the Cave of Cruachan, which is well-known across Irish storytelling traditions (myth, legend, folklore, and fairytale) as a portal to the Otherworld.

These days, Cruachan is better-known as Rathcroghan (Irish: Ráth Cruachan), meaning “fort of Cruachan.” It’s an archaeological site—or a collection of multiple archaeological sites, really—which, intriguingly, includes a limestone cave called the Uaimh na gCat, or “Cave of the Cats.” There’s also an earthen mound nearly 90 meters (295 feet) in diameter, with an enclosure quadruple that size (360 meters in diameter) hidden beneath it. 

Can’t you picture it? That reptilian behemoth exploding from beneath the earth, unfurling its wings, preparing to wreak havoc on the countryside…its three sets of jaws snapping in anticipation.

Never mind the fact that the “cave” beneath Rathcroghan mound is only 5 meters (16 feet) deep. The larger problem with this vision is that most texts and academics describe Ellén Trechend not as some sort of three-headed oilliphéist, but as a giant bird-monster.

For example, Celtic scholar Whitley Stokes described Ellén Trechend as a “monstrous triple-headed bird.” Stokes also suggested that the name Ellén was derived from the Old Irish word for bird, én (source: “The Battle of Mag Mucrime”, Revue Celtique 13, 1892).

(FYI: the “Trechend” part of the name literally means “three-headed.” Compare with the modern Irish: trí-cheann.)

Writing more than a century later, author Daragh Smyth offers the following etymology: 

“Éli in Irish means ‘a charm or a chant or an incantation’, and the goddess associated with the Éli may be the ellen trechend or the triple-headed goddess who sometimes assumes the form of a destructive bird.”

source: Earthing the Myths: The Myths, Legends and Early History of Ireland (2020)

Indeed, in almost all modern descriptions, Ellén Trechend has avian—not reptilian—characteristics. Here’s the entry for the monster in Austin Hudson’s A Field Guide to Strange Things (2019):

“An enormous, monstrous three-headed bird that is frequently referenced as having been a blight on Ireland prior to its death. Said to possibly breathe fire. Traveled in a swarm with smaller birds, creating a path of destruction wherever they went.”

And here how Ellén Trechend is described in Nicolle R. Murray’s Naturally Monstrous and Magical Creatures of Australia and the Islands of the World (2019): 

“A monsterous, 3 headed vulture-like bird. Copper red in color…Appears on Halloween. When it emerges, it lays waste to the countryside until stopped.”

So, case closed on this one, right?

Ellén Trechend is a massive, three-headed monster—only its appearance is probably a bit different from what you had originally pictured. Fewer scales; more feathers. Fewer teeth; more beaks. But hey, the wings are a constant. Clearly they were able to carry over as the popular image of Ellén Trechend evolved.

The only issue with the giant-bird-monster interpretation of Ellén Trechend:

It clashes with the story in which Ellén Trechend is introduced: Cath Maige Mucrama, or the Battle of Mag Mucrama. 

In the translation I looked at (source: AncientTexts.org), the monster and its slayer—warrior-poet Amergin mac Eccit of the Ulaid over-kingdom (not to be confused with the Milesian druid Amergin)—are mentioned only in passing. And I quote:

“Now Mag Mucrima [was so called from] magic pigs that had come out of the cave of Crúachain. That is Ireland’s gate to Hell. Out of it too came the swarm of three-headed creatures that laid Ireland waste until Amairgene father of Conall Cernach, fighting alone (?), destroyed it in the presence of all the Ulaid.

“Out of it also had come the saffron-coloured(?) bird-flock and they withered up everything in Ireland that their breath touched until the Ulaid killed them with their slings.”

Whoa. 

This Ellén Trechend is an entirely different beast. Literally. A tiger of a different stripe…not so literally.

Instead of a single monster with three heads, the text presents us with “a swarm of three-headed creatures.” What’s more, this battle between Amerigin (a.k.a. Amairgen) and the swarm is immediately followed by a story about a flock of “saffron-coloured” birds that “withered up everything in Ireland that their breath touched.”

So now we’ve got a flock of fire-breathing birds and a swarm of (presumably bird-sized?) three-headed monsters. It’s easy to see how, over time, storytellers might end up combining these two supernatural forces into a single, cohesive enemy, either intentionally or unintentionally.

I’d argue that there’s also a natural tendency—as I’ve discovered while telling bedtime stories to my children—to make monsters bigger with each retelling of a story. Hence, a bunch of little monsters morphing into a single, humongous monster seems like a natural evolution of the character.

Speaking of which…

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5. Aillén mac Midhna

I nearly excluded Aillén mac Midhna (also: Midna, Midgna) from this list primarily because I’ve written about him so much already. I tell the story of Fionn mac Cumhail defeating the fire-breathing, Otherworld monster in Irish Myths in Your Pocket and, because it takes place on Samhain, in Samhain in Your Pocket. 

What’s more, even with the generous editorial approach I’ve taken while constructing this list, I struggle to call Aillén a dragon. Apart from the fire-breath, there’s nothing draconic about him. Yes, if illustrations are to be believed, he’s huge—a giant. But he’s basically humanoid in design.

Basically.

In Heroes of the Dawn (1914), author Violet Russell describes Aillén as an “unconquerable enchanter” and a “magician.” He’s more man than monster. 

But we have to remember, Aillén did climb out of the Cave of Cruach—just like so many monsters before him.

Yes, it’s called the Cave of Cruach in the Fenian Cycle of Irish mythology, whereas in the chronologically earlier Ulster Cycle tales, it’s called the Cave of Cruachan. But I think it’s safe to say they’re the same cave.

And according to Irish linguist T. F. O’Rahilly, it’s also safe to assume that the aforementioned Ellén is effectively the same monster as Aillén, hence the similarities in their names and incendiary capabilities (source: Early Irish History and Mythology, 1946).

It’s possible Aillén represents the latest stage in the evolution of Ellén—its final form. More intelligent. More human.

And once again, we see a storytelling formula at work. You can swap out Ellén for Aillén and/or Amergin for Fionn at your leisure and the overarching narrative will remain the same.

In fact, in one version of the story, that’s exactly what happens. To quote Ellis:

“In one of the several variants [of the Aillén story], Amairgen is given as the slayer of the beast.”

source: A Dictionary of Irish Mythology (1987)

And while Aillén would go on to become one of the most infamous Otherworld creatures, he would by no means be the last monster to crawl out of the Cave of Cruachan.

In addition to three-headed monsters and a trio of giant cats, the cave is also home to another supernatural triad: the three daughters of Airitech…

Ireland’s first werewolves.

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Want to meet more monsters from Irish mythology? Check out…

Irish Monsters in Your Pocket (Celtic Pocket Guides 3)

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Neon Druid: An Anthology of Urban Celtic Fantasy

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Want to learn the full story of Samhain? Check out…

Samhain in Your Pocket (Celtic Pocket Guides 2)

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More the listenin’ type?

I recommend the audiobook Celtic Mythology: Tales of Gods, Goddesses, and Heroes by Philip Freeman (narrated by Gerard Doyle). Use my link to get 3 free months of Audible Premium Plus and you can listen to the full 7.5-hour audiobook for free.

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Last thing, I promise:

Introducing the official Irish Myths YouTube channel. Same Celtic flavor, new bold format.