Differences Between Irish and Celtic Mythology

CELTIC COGNATES chart showing parallels between different Celtic deities

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While you often hear the two terms used interchangeably, are Irish mythology and Celtic mythology the same thing? 

The short answer: No. They’re different 

The longer answer: While they’re not synonyms, Irish mythology and Celtic mythology are connected.

There are two ways we can think about this, and that’s because there are two ways one can interpret the meaning of Celtic mythology.

Now, if the first thing that pops into your head when you think of Celtic mythology is a dude with gigantic antlers sprouting out of his skull then you’re effectively interpreting Celtic mythology to mean Gaulish mythology.

Ancient Gaul, which consisted of modern-day France, Belgium, northern Italy, western Switzerland and parts of the Netherlands and Germany, was the home turf of the Gaulish- or Gallic-speaking Celts.

That dude with the antlers, who’s often depicted wearing a torc and sitting cross-legged?

He’s the ancient Celtic/Gallo-Roman nature god Cernunnos.

And while there are dozens of depictions of Cernunnos spread across Europe the overwhelming majority of them appear in northeastern Gaul.

Indeed there is a whole pantheon of deities centered in Gaul, including Taranis, god of thunder, who’s been called the Gaulish Jupiter; Toutatis, tribal protector-god, a.k.a. the Gaulish Mars; Ogmios, god of eloquence/club-wielding hero who’s been described as an older version of Hercules; Lugus, the many-skilled god who’s been called the Gaulish Mercury; Belenus, who may or may not be a sun-god but regardless he’s been called the Gaulish Apollo (FYI: you can learn more about Belenus in my article (and video) on the Celtic May Day festival Beltane, which may or may not have been named after the god Belenus. But I digress); Gobannus, the smithing god, comparable to Vulcan; Sucellus, god of agriculture and prosperity who’s been called the Gaulish Dis Pater; and Epona the horse goddess—and possible leader of souls (a.k.a. psychopomp)—whose cult became so popular that, between the first and third centuries CE, she was worshiped not only across the Roman Empire but in Rome itself.

Now, it is absolutely valid to refer to the aforementioned gods as Celtic gods. And by extension it’s valid to refer to stories about said gods as Celtic mythology.

The ancient Gauls were Celtic-speakers after all.

What’s more, for much of antiquity, the Gauls were the Celts. At least according to their Greco-Roman neighbors.

As archaeologist Barry Cunliffe notes in his book Druids: A Very Short Introduction, in Classical texts, “the names ‘Gauls’ and ‘Celts’ were often used interchangeably.”

Granted, the ancient Gauls didn’t really write much down, which was due in large part to a druid-enforced taboo on writing down sacred knowledge. 

So most of the information we have concerning the mythical exploits and interminglings of Gaulish deities—like the horned god Cernunnos and the horse goddess Epona and the agricultural god Sucellus, from whom, the Gauls believed, all Gauls were descended (will that be important later? maybe…)—comes from surviving inscriptions and descriptions given by Classical writers and conquerors, like Julius Caesar.

Regardless, when we take this view of Celtic mythology, with its focus on the Gaulish pantheon, it’s easy to see what makes it different from Irish mythology:

Irish mythology is…from Ireland.

Its stories are set, for the most part, in and around Ireland.

And it has its own pantheon of Irish deities, separate from the Gaulish ones, known as the Tuatha Dé Dannan.

Members of the Tuatha Dé Dannan include the  Morrígan, triple goddess and goddess of battle; Ogma, the god of language and eloquence; Lugh, the god of many talents; Bilé, god of death; Goibniu, the smith god; the Dagda, the father of the Irish gods, from whom all the gods were descended; Manannán mac Lir, the sea-god; and Nuada Airgetlam, the silver-handed leader of the Tuatha Dé Dannan.

You know, deities that are distinctly Irish with no…uh…wait, what’s happening? What’s going on with that chart?

chart showing comparisons between welsh irish and gaulish gods

Oh, right. You see, some of the Irish gods have parallels or cognates with the aforementioned Celtic gods.

Which makes sense given that the mythology of Ireland, or at least the version we inherited, was created by…Celts.

Different Celts. These were Gaelic- or Goidelic speakers. Not Gaulish- or Gallic-speaking Celts. But Celts nonetheless.

And when their Celtic language and culture arrived in Ireland, likely during the Iron Age, new meanings were attached to the dolmens and tumuli that had adorned the Irish landscape since the Stone Age.

These megaliths became the homes of the gods and portals to the Otherworld.

That’s essentially how Irish mythology was born. 

And that leads us to the second way one can think about Celtic mythology. 

Because if Irish mythology is also an ancient Celtic storytelling tradition concerning the activities of divine beings, which it is, then one could easily make the argument that Irish mythology is a form of or subcategory of Celtic mythology.

And I wouldn’t argue with that.

In fact, I’ll gladly make the argument for that. 

Celtic Mythology: The Ultimate Umbrella Term

At the end of the day, or the Iron Age, as it were, Irish mythology can be considered a branch of Celtic mythology similar to how Catholicism is a branch of the broader religious tradition of Christianity.

No, that’s not a perfect analogy, but the takeaway is that Celtic mythology can be used as an umbrella term to refer to all of the mythologies of the different Celtic tribes. 

So in addition to the Gaulish-speaking Celts who lived in Gaul and the Gaelic-speaking Celts who settled in Ireland, Scotland, and the Isle of Man, you’ve got the Brittonic-speaking Celts who settled in Wales, Cornwall, and Brittany; the Boii who lived in what is now Northern Italy and Austria and Hungary and the Czech Republic; the Celtiberians who lived in what is now central Spain; the Gallaeci in Portugal and Galicia and western Asturias; the Galatians in Turkey; and the Lepontii up in the Alps.

Yes, all of those tribes spoke Celtic languages—languages that originated with a common proto-Celtic progenitor. 

And language, of course, is elemental to what it means to be Celtic.

Quick tangent:

The Celts were not a continuous lineage of people, meaning, for example, that the Gaelic-speakers who settled in Ireland were not genetic descendants of the original, proto-Celtic peoples who emerged in Central Europe in the Late Bronze Age.

Celtic isn’t a race or ethnicity—it’s a culture.

And we can map the spread of that culture both through language and mythology. 

The Gauls, the Gaels, the Britons, the Boii, the Celtiberians, the Gallaeci, the Galatians, the Lepontii—they all practiced some form of what scholars call the Ancient Celtic religion, more commonly known as Celtic paganism.

And while in the majority of cases (don’t worry, we’ll get to the exceptions), there are no surviving written accounts of the Celtic mythologies (plural) associated with these religions, we can still glean their existence from archaeological evidence.

An altar depicting a three-faced god identified as Lugh/Lugus
An altar depicting a three-faced god identified as Lugh/Lugus

And, we can speculate based on what we find in the manuscripts that have survived—specifically those associated with the Irish and Welsh traditions. 

Indeed when we look at Irish mythology and Welsh mythology side by side, we find many similarities between their characters and narratives, despite the fact that one came from a Gaelic Celtic tradition and the other from a Brittonic Celtic tradition.

For example, the famed Irish hero Fionn mac Cumhaill has a parallel in the Welsh hero Gwynn ap Nudd.

In Old Irish fionn meant white or fair, while in Old Welsh gwynn meant the same thing (white or fair). Same word, different Celtic language.

This pattern continues with the Irish sea-god Manannán mac Lir (“Mac Lir” meaning “son of the sea”) who has a watery Welsh doppelganger in Manawydan fab Llŷr. 

Then there’s the leader of the Irish gods Nuada Airgetlam (Nuada of the Silver Arm or Hand) who has a parallel in the Welsh character Nudd Llaw Ereint, Nudd of the Silver Arm or Hand, who, in the myths, ruled all of Britain.

It’s likely that Nuada and Nudd (later called Lludd) were both derived from an earlier Celtic god Nodens who was worshiped in pre-Roman Britain.

And I’d be remiss not to mention that a one mister Mr. J. R. R. Tolkien once visited the ruins of a temple to Nodens located at Dwarf’s Hill, a site known for its network of tunnels and iron deposits and inscriptions that talk about a cursed ring.

You can’t make this up. Well, I mean, you can. You know what I mean.

As far as I can tell, it was Tolkien who first drew the connection between Nodens and the Irish Nuada of the Silver-Hand, who in turn inspired Tolkien’s character Celebrimbor, the Elven-smith, whose name means—you guessed it—silver hand.

Anyway the point I was trying to make before I went off down this hobbit hole is that there is clearly some connective tissue between Welsh and Irish and Gaulish mythologies.

The Welsh Rhiannon, the Irish Morrigan, the Gaulish Epona: possible cognates.

The Welsh Eufydd fab Dôn, the Irish Ogma, the Gaulish Ogmios: possible cognates.

The Welsh Llew, the Irish Lugh, the Gaulish Lugus: possible cognates.

The Welsh Beli Mawr, the Irish Bile, the Gaulish Belenus: possible cognates.

The Welsh, the Irish Goibniu, the Gaulish Gobannus: possible cognates.

Now, originally I envisioned the Gauls as sort of being the founders of Celtic mythology, who then passed the torch onto the Irish and Welsh.

However, when we look at how the different Celtic languages actually evolved, branching off from proto-Celtic, regardless of whether you go with the P-/Q-Celtic classification system or the insular/continental classification system, the end result is the same:

Like the Irish language itself, which evolved independently of the Gaulish language, Irish mythology likely evolved independently of Gaulish mythology.

chart showing two different versions of the celtic language tree (both of which begin with proto-celtic

And this points to the likelihood that there was once a common Celtic mythology—or proto-Celtic mythology—that went hand-in-hand (or word-for-word?) with the proto-Celtic language.

To quote historian Peter Berresford Ellis’ A Dictionary of Irish Mythology:

“The fact that one can see relationships and counterparts demonstrates that Irish mythology is not a separate entity from the rest of the Celtic world. In it we find echoes of a common Celtic mythological, religious and, perhaps, historical experience.”

Irish Mythology: The Best Preserved Form of Celtic Mythology

Historian Thomas Cahill famously argued that following the collapse of the Roman Empire, the Irish effectively saved Western Civilization by copying and preserving important texts. 

Imagine an Irish monk, up in his stone tower, surrounded by ink and vellum. He’s pulled up his ladder to prevent Viking marauders from getting inside.

It’s probably no exaggeration to say that actions such as these helped preserve Irish mythology for future generations. 

Now, did the Christian scribes who recorded the Irish myths we now know and love today take a few liberties here and there?

Of course they did.

The Christian influence is readily apparent in the texts.

Just take a look at the Lebor Gabála Érenn, or “The Book of the Taking of Ireland”—often referred to as the Book of Invasions.

Dated to the 11th century, the book details the arrivals of the different mythical races of Ireland and concludes with the Milesians—Celtic-speakers from Spain—displacing the Irish gods, the Tuatha De Dannan, and sending them underground.

"The Coming of the Sons of Miled", illustration by J. C. Leyendecker in T. W. Rolleston's Myths & Legends of the Celtic Race, 1911
“The Coming of the Sons of Miled”, illustration by J. C. Leyendecker in T. W. Rolleston’s Myths & Legends of the Celtic Race, 1911

But interestingly, the Lebor Gabála Érenn tells us that Ireland’s very first wave of settlers is led by Noah’s granddaughter, Cessair, who also lends that group their name: the Cessair.

And yes by Noah I mean Old Testament Noah with the flood and the ark and the animals.

In other texts it’s shown that the hero Fionn mac Cumhaill’s lineage can be traced back to Míl Espáne King of Spain, namesake of the Milesians, and back to Queen Scota of Egypt, namesake of the country Scotland, and all the way back to Adam and Eve.

Later, Fionn’s son Oisín, Ireland’s greatest poet who disappeared to Tir na nÓg (the land of the young) for 300 years, can be found rubbing elbows with none other than Saint Patrick.

So yeah, while Christian monks did much to preserve Irish mythology, it’s obvious that what they handed down to us isn’t the purest form of this Celtic storytelling tradition.

As with other Celtic peoples, it seems the Gaels in Ireland–and specifically their druid class–had a taboo against writing down sacred knowledge. Thus, their religious stories were only shared orally prior to the arrival of Christianity. 

To quote Celtic scholar Georges Dottin:

“It is probable that the most ancient pieces of the epic literature of Ireland were written before the middle of the seventh century; but how long previously they had been preserved by oral tradition — this is a point that is difficult to estimate.”

The Four Cycles of Irish Mythology 

Today, scholars organize Irish mythology into four distinct chronological phases, or cycles:

The Mythological Cycle, the Ulster Cycle, the Fenian Cycle, and the King Cycle.

Let’s run through them one by one:

1. The Mythological Cycle

Stories in the Mythological Cycle concern themselves primarily with the various races of gods and god-like people who successively invade and inhabit Ireland in the pre-Christian era. 

These are, in order, the Cessair, the Partholónians, the Nemedians, the Fir Bolg, the Tuatha Dé Danann, and the Milesians.

And of course just like a phase in a modern cinematic universe, every storytelling cycle needs its big bad.

In the case of the Mythological Cycle, that’s Balor of the Evil Eye, a monster with a humongous fiery eye that can vaporize entire armies.

Balor is the leader of the Fomorians, who originated from beneath the earth and yeah if this is all starting to sound familiar it’s because Tolkien read all of this stuff too. 

Think about it: the Tuatha Dé Danann are the mystical Elves who recognize that the Age of Men (the Milesians) is upon them so they must go to Valinor, “the Undying Lands”, which sounds an awful lot like Tir nan Og, the land of youth.

Anyways, the survival of these myths hinges largely on two medieval manuscripts: the aforementioned Lebor Gabála Érenn and the Metrical Dindshenchas (Lore of Places).

Popular stories from the Mythological Cycle include the Children of Lir, which sees the titular Tuatha Dé Danann sea-god (and inspiration for Shakespeare’s King Lear) fathering four children who are turned into swans by his jealous second wife; and The Wooing of Étain, in which the titular princess falls in love with the god Midir of the Tuatha Dé Danann but then his angry ex transforms Étain into a bejeweled fly. 

Yeah, there’s a whole lot of transforming into animals in this cycle and in Irish mythology in general. 

Speaking of animals: Étain is sometimes given the epithet Echraide, meaning “horse rider”, suggesting a possible connection to the Gaulish Epona and the Welsh Rhiannon.

2. The Ulster Cycle

The Ulster Cycle a.k.a. the Red Branch Cycle concerns the warriors, known as the Red Branch, who defend Ulster during the reign of Conchobhar Mac Nessa. 

The main stories of the cycle comprise the epic Táin Bó Cúailnge, which has been described as the Irish Illiad

The Táin, as it’s known for short, sees Queen Medb and her husband King Ailill of Connacht wage war against Ulster all for the sake of the prized stud Donn Cúailnge, the Brown Bull of Cooley.

The primary hero of this cycle is Cú Chulainn, the Hound of Culann, also called the Hound of Ulster, who is sometimes compared to Achilles but who is definitely more like the Irish hulk.

The myths of the Ulster Cycle are preserved in two 12th-century texts: the Leabhar n hUidre (Book of the Dun Cow) and the Leabhar Laigeneach (Book of Leinster).

3. The Fenian Cycle

The Fenian Cycle chronicles the adventures of the hero Fionn Mac Cumhail and the Fenians, also known as the Fianna, who were a band of warriors responsible for guarding the High King of Ireland.

Within the Fenian Cycle we find the Macgnímartha Finn, or boyhood deeds of Fionn, a collection of stories chronicling the hero’s rise from forced exile and fosterhood to him feasting on a supernatural fish (the Salmon of Knowledge), to Fionn—as a ten-year-old!—defeating a fire-breathing, literally Otherworldly monster with a magical spear on Samhain, thus saving Tara (the seat of the High King) from certain destruction.

Fionn fighting Otherworld creature with magic spear
Fionn fighting Aillen, illustration by Beatrice Elvery in Violet Russell’s Heroes of the Dawn (1914) (source: Wikimedia Commons)

But arguably the most famous story from the Fenian Cycle, the Pursuit of Diarmuid and Gráinne, is set chronologically much later, when Fionn is an old man.

In the story, Gráinne, Fionn’s betrothed, runs off with a young, dashing warrior of the Fianna, Diarmuid Ua Duibhne, or Diarmuid of the Love Spot, foster-son of the love-god Aengus.

Shenanigans ensue.

Including Diarmuid meeting his demise at the sword, no, sorry make that at the tusk of his step-brother who had been turned into a magical boar.

Note: The Fenian Cycle is also known as the Ossianic Cycle after the cycle’s supposed author, the aforementioned Oisín.

4. The King Cycle

Also known as the Cycle of the Kings or the Historical Cycle, the King Cycle blurs the lines between history and myth more so than any of the earlier cycles.

Geared toward providing examples of how to be a good ruler, the cycle features the likes of real historical figures, such as the Irish king Brian Boru, born in 941 CE, as well as purely mythological ones, such as Labraid Loingsech (or Loinseach), the Mariner Who Speaks, who, according to Irish legend, was an exiled High King of Ireland who lost the ability to speak after eating his father’s heart.


One of the most popular stories of the cycle is Buile Shuibhne, The Frenzy of Sweeney (or The Madness of Sweeney). 

The story tells of a king of the Dál Riada (or Riata), Suibhne Geilt, who, after fleeing a battle, journeys through Ireland’s wild places in search of peace of mind.

This Irish character might have helped inspire Merlin from Arthurian Legend but it’s still up for debate. 

FYI: I wrote a series of essays about Sweeney and Merlin and Myrridin and the origins of the Celtic wild man of the woods motif.

Another Approach to Categorizing Irish Myths

While the “four cycles” approach to Irish myth categorization has become ubiquitous in the study of Irish mythology, it can be a bit confusing since the Irish gods ( i.e., the Tuatha Dé Danann) and their descendants can and do appear across multiple cycles.

The Morrigan, for example, after playing a significant role in the Mythological Cycle, goes on to effectively haunt the hero Cu Chullain during the Ulster Cycle, and is a witness to his death.

Cúchulainn statue in the General Post Office
In commemoration of the 1916 Easter Rising, a statue depicting the death of the mythical hero Cúchulainn sculpted by Oliver Sheppard in 1911 is displayed in the front window of the GPO. (credit: Jennifer Boyer, Flickr)

True, while some particular stories may veer more into legend or folktale or even history territory, myths (naturally) abound across all four cycles of Irish mythology.

Which is why it’s so weird that the first cycle of Irish mythology is called the “Mythological” Cycle.

And here’s the thing: It hasn’t always been like this.

Prior to the adoption of the four cycles, chroniclers of Irish mythology organized stories into two main categories, prim-scéil (chief tales) and fo-scéil (minor tales).

According to Ellis, prim-scéil stories included battles, voyages, tragedies, adventures, military expeditions, courtships, elopements, concealments, destructions, sieges, feasts, slaughters, and cattle-raids—there were a lot of cattle-raids.

Whereas the fo-scéil included pursuits, visions, exiles/banishments, and lake-bursts. 

The lake-burst or tomhaidhm in Irish is both a natural—make that supernatural—phenomenon as well as a genre of bardic story in which a lake or bay or other body of water just sort of bubbles up out of nowhere, often when someone is digging a grave.

Granted the most famous lake-burst from Irish mythology, arguably, occurs at Lough Neagh as a result of a giant magical horse, a gift from the aforementioned love-god Aengus, taking a pee.

Which reminds me: Aengus, who also goes by the moniker Mac Óg (“young son”), has a likely cognate in the Welsh mythical figure Mabon ap Modron, as well as in the Gaulish god Maponos, a.k.a. the Great Son.

chart showing comparisons between welsh irish and gaulish gods

But back to the lake eruptions.

Turns out they’re also a pretty common story category across the Celtic world—or at least the Atlantic Celtic world—with examples appearing in medieval manuscripts in Wales, Cornwall, Brittany, and Normandy.

And no while Normandy is not considered a bastion of Celtic culture in the same way that Ireland, Wales, Cornwall, and Brittany are, (alongside Scotland and the Isle of Man and occasionally Galicia and Asturias they’re considered the six or eight modern Celtic nations), Normandy was, for much of its history, teeming with Gaulish tribes.

So once again we find another possible link connecting the mythologies of Gaulish-speaking Celts, Brittonic-speaking Celts, and Gaelic-speaking Celts.

And once again we catch a glimpse of a theoretical common Celtic mythology that would ultimately seed the creation of Irish mythology.

Want to learn about the darker side of Irish and Celtic mythology? Check out…

Samhain in Your Pocket (Celtic Pocket Guides 2)

Perhaps the most important holiday on the ancient Celtic calendar, Samhain marks the end of summer and the beginning of a new pastoral year. It is a liminal time—a time when the forces of light and darkness, warmth and cold, growth and blight, are in conflict. A time when the barrier between the land of the living and the land of the dead is at its thinnest. A time when all manner of spirits and demons are wont to cross over from the Celtic Otherworld. Learn more…

Irish Monsters in Your Pocket (Celtic Pocket Guides 3)

In the Ireland of myth and legend, “spooky season” is every season. Spirits roam the countryside, hovering above the bogs. Werewolves lope through forests under full moons. Dragons lurk beneath the waves. Granted, there’s no denying that Samhain (Halloween’s Celtic predecessor) tends to bring out some of the island’s biggest, baddest monsters. Prepare yourself for (educational) encounters with Irish cryptids, demons, ghouls, goblins, and other supernatural beings. Learn more…

Neon Druid: An Anthology of Urban Celtic Fantasy

“A thrilling romp through pubs, mythology, and alleyways. NEON DRUID is such a fun, pulpy anthology of stories that embody Celtic fantasy and myth,” (Pyles of Books). Cross over into a world where the mischievous gods, goddesses, monsters, and heroes of Celtic mythology live among us, intermingling with unsuspecting mortals and stirring up mayhem in cities and towns on both sides of the Atlantic, from Limerick and Edinburgh to Montreal and Boston. Learn more…

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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