What Is Irish Mythology? (And How Is It Different From Celtic Mythology?)

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

The short answer: No.

The longer answer: While they’re not exactly synonyms, Irish mythology and Celtic mythology are inexorably linked, with the former (Irish) being a branch of the latter (Celtic), similar to how Catholicism is a branch of the broader religious tradition of Christianity.

How do we know this? Because when we look at the gods of the ancient Celts who inhabited Gaul (modern day France, Belgium, Luxembourg, and parts of the Netherlands, Switzerland, Germany, and Northern Italy) prior to Romanization, we see unmistakable counterparts, or cognates, in the gods of their Irish descendants. And it wasn’t just the Irish who inherited these Celtic gods: The Scottish, Cornish, Manx, Breton, and Welsh descendants of the Gaulish Celts inherited them as well, as they—like the Irish—all inhabited the western fringes of Europe, out of reach of Roman influence.

For example, the god Lugh (or Lug) from Irish mythology and the god Lleu (or Llew) from Welsh mythology are both clearly derived from the same Gaulish sun god Lugus (or Lugos). Same with the Irish god Ogma (or Oghma) and the Welsh god Eufydd fab Dôn, who are both derived from Ogmios, the Gaulish god of eloquence.

To quote historian Peter Berresford Ellis:

“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.”

(A Dictionary of Irish Mythology, 1987)

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What Is Celtic Mythology? A Definition:

Celtic mythology is the body of traditional stories and teachings of the ancient Celts, concerning their gods, heroes, and the origins of their world. These myths were a part of an ancient Celtic polytheistic religion, which, along with the Celts themselves, had spread across much of Western Europe and as far east as modern-day Turkey. 

As an oral tradition, Celtic mythology did not enter the written record until the Romans began their conquest of Gaul, Iberia, and other strongholds of Celtic culture. The ensuing Romanization of Celtic lands effectively rendered Celtic mythology extinct, at least in its original form. However, on the western seaboard of Europe, including Ireland, the mythology of the Celts would continue to flourish and evolve.

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What Is Irish Mythology? A Definition:

Irish mythology is the most well-preserved form of Celtic mythology, consisting of traditional stories and teachings that originated with the pre-Christian ancient Gaels (Goidelic-speaking Celts) who arrived in Ireland between 500 and 300 BCE. (For context, Ireland’s very first inhabitants arrived between 7,000 and 6,500 BCE.)

Upon reaching Ireland, the Gaels encountered massive stone structures (dolmens and cairns) and earthen burial mounds (tumuli), which, in addition to the natural wonders of the Irish landscape, inspired new stories and beliefs that would be grafted onto their existing Celtic polytheism. The burial mounds, for example, were interpreted as portals to the Celtic Otherworld: land of the gods.

Today, scholars and academics organize Irish mythology into four distinct chronological phases, or cycles.

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The Four Cycles of Irish Mythology

1. The Mythological Cycle

The Mythological Cycle details the various gods and god-like people who inhabited and invaded Ireland in the pre-Christian era, from the Fomorri to the Nemedians to the Firbolg to the De Danaan to the Milesians.

The survival of these myths hinge largely on two works written between the 10th and 14th centuries CE: the Lebor Gabála Érenn (Book of Invasions) and the Metrical Dindshenchas (Lore of Places). Popular stories from the Mythological Cycle include The Wooing of Étain, The Dream of Aengus, and the Children of Lir.

2. The Ulster Cycle

The Ulster Cycle concerns the warriors, known as the Red Branch, who defended Ulster during the reign of Conchobhar Mac Nessa. Also known as the Red Branch Cycle, the main stories of the cycle comprise the epic Táin Bó Cúailnge, which has been described as the Irish Illiad.

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. 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 Fionn Mac Cumhail (anglicized as Finn McCool or MacCool) and the Fenians, also known as the Fianna, who were a band of warriors responsible for guarding the High King of Ireland.

One of the most popular stories of the cycle is the Salmon of Knowledge, in which a fish (Fintan) eats of the Nuts of Knowledge before being caught by the druid Finegas. The druid gives Fionn Mac Cumhail the fish to cook, and Fionn subsequently burns his thumb on the fish’s flesh. Upon sucking his thumb, Fionn acquires wisdom. Another popular story in the cycle is the Pursuit of Diarmuid and Gráinne, in which Fionn’s bride-to-be (Gráinne) runs off with one of his warriors (Diarmuid Ua Duibhne).

Note: The Fenian Cycle is also known as the Ossianic Cycle after the cycle’s supposed author, Oisín, Ireland’s greatest poet and the son of Fionn.

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 Sweeny (or The Madness of Sweeney). The story tells of a warrior, Duibhne of the Dál Riada (or Riata) who, after being injured in battle, journeys through Ireland’s wild places in search of peace of mind.

Another Approach to Categorizing Irish Myths

While the above categorizations have become ubiquitous in the study of Irish mythology, they can be a bit confusing since characters from one cycle often turn up in other cycles. What’s more, the Irish gods are a constant throughout all of the cycles, and all of the stories in the four cycles (to a greater or less extent) are myths, which makes the name of the first cycle, the Mythological Cycle, particularly misleading. 

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). The prim-scéil stories included battles, voyages, tragedies, adventures, cattle-raids, military expeditions, courtships, elopements, concealments, destructions, sieges, feasts, and slaughters, while the fo-scéil included pursuits, visions, exiles or banishments, and lake eruptions.

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Putting Quill to Vellum: The Christian Influence on Irish Mythology

Up until the arrival of Christian missionaries in Ireland (400 – 450 CE), Irish mythology (and more broadly, Celtic mythology) remained an oral tradition. 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.”

While Christian monks did much to preserve Irish mythology, it was not always easy for them to grant divinity to Celtic/Irish gods and heroes on the written page, and thus many deities and divine figures of Irish mythology were downgraded to evil spirits or mere mortals. 

For a more accurate understanding of what the ancient, pre-Christian Irish actually believed, consider this quote from historian Peter Berresford Ellis:

“Certainly Irish mythology is essentially an heroic one and the Irish do appear to have made their heroes into gods and their gods into heroes. In the lives of these gods and heroes, the lives of the people and the essence of their religious traditions are mirrored.”

(A Dictionary of Irish Mythology, 1987)

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Who Were the Gods and Heroes of Irish Mythology?

During the 17th and 18th centuries, the English sought to eradicate Irish culture, language, and myths, and many of the books and manuscripts penned by Irish monks were destroyed. However, for much of Ireland’s population at this time, these written accounts were not well-known. To quote Ellis:

“Irish mythology had become a mere folkloric tradition, tales recited by the village story-teller (the seanchai) around the hearth at night, their origin and symbolism forgotten.”

(A Dictionary of Irish Mythology, 1987)

Irish folklore further eroded the status of Celtic/Irish gods, reimagining them as fairies and little people. Lugh, for example, once one of the most important gods in the Celtic pantheon, became “little stooping Lugh,” or Lugh-chromain (anglicized as “Leprechaun”).

The hills and tumuli that dot the Irish countryside, meanwhile, were reinterpreted as fairy mounds, the dwelling places of the Tuatha Dé Danann (the ancient gods, including Lugh, who, according to Irish myth, were driven underground by the invading Milesians). In Old Irish, sídhe was the word for hill or tumulus. The aes sídhe, fairies, are the people of the hills. And the most famous (or infamous) of the aes sídhe is the bean sídhe, the woman of the fairies, better known as the banshee.

To the ancient Irish, however, their Celtic-descended gods were not fairies or little people or shrieking evil spirits. They were much more… well… god-like (at least per European standards of divinity).

The gods of Irish myth were tall, strong, attractive, fair-skinned, and more powerful than your average human. According to Ellis, “They are somewhat reminiscent of the description of the ancient Celts which survive in the writing of Greeks and Romans.” This is an especially fitting comparison when one considers that the gods of Irish mythology were viewed not as the creators of Irish people, but as their ancestors. 

Another distinguishing feature of the Irish gods and heroes: They could shapeshift, turning into all manner of animal in order to trick or evade. A prime example of shapeshifting in Irish mythology can be seen in the story of Tuan Mac Cairell, who survived a plague by turning into a deer, and after reaching old age turned into an eagle, before turning into a salmon. The salmon was caught and eaten by Tuan Mac Cairell’s wife, who then gave birth to him in human form, his memories in tact.

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Eternal Life and Reincarnation in Celtic Myth

In addition highlighting an example of shapeshifting in Irish mythology, the story of Tuan Mac Cairell (summarized above) typifies both the ancient Irish belief and broader ancient Celtic belief in reincarnation. And here we have yet another religious through-line from the Gaulish Celts to their Goidelic-speaking descendants.

The Celts were one of the first peoples in Europe to believe in the immortality of the soul. According to their religious doctrine, death was not the ultimate end, but merely a transition to another world—the world of the dead—where life continued more or less as usual, with all of the same comforts and activities. To quote Ellis:

“A constant exchange of souls was always taking place between the two worlds; death in this world brought a soul to the Otherworld and death in the Otherworld brought a soul to this world.”

(A Dictionary of Irish Mythology, 1987)

It was also believed that one night a year (October 31st / November 1st), the barriers between the two worlds became permeable, and the “dead” were able to cross over and wreak havoc on the living world. The ancient Celts celebrated this event as the Feast of Samhain, and the tradition, surviving Christianization, continues to this day on November 1st as All Saints’ Day, also known as All-Hallows Day. And of course, All-Hallow’s Eve (better known as Halloween) is celebrated the night before, on October 31st.

The Celtic doctrine of eternal life was also seen as an explanation for the fighting prowess of the ancient Celts, whose fearlessness in battle was renowned all over the ancient world—so much so that the ancient Greeks likely borrowed the concept of the immortal soul from the Gaulish Celts and incorporated it into their own belief system back in the second century BCE, if not before.

So as you can see, the beliefs of the Gaulish Celts influenced not only the mythologies of their direct Irish descendants, but of Europeans as a whole.

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Further Reading

How the Irish Saved Civilization by Thomas Cahill

A Dictionary of Irish Mythology (Oxford Reference) by Peter Berresford Ellis

Dictionary of Celtic Mythology (Oxford Reference) by Peter Berresford Ellis

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

Samhain in Your Pocket (Celtic Pocket Guides 2)

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Neon Druid: An Anthology of Urban Celtic Fantasy

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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.