Irish Mythology: History and Legacy

Ancient sacred tomb in Ireland
Ancient sacred tomb in Ireland.

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Irish mythology is a collection of pre-Christian beliefs detailing the histories and legends of ancient Ireland. These beliefs include descriptions and stories of deities, heroes, and kings measured in four distinct, chronological cycles. 

Key Takeaways

  • Irish mythology is a branch of Celtic mythology detailing the legends and histories of ancient Ireland. 
  • It includes four distinct chronological cycles: Mythological, Ulster, Fenian, and Historical.  
  • The oldest of these, the Mythological Cycle, details the supernatural first inhabitants of Ireland, known as the Tuatha Dé Dannan. 
  • These myths and legends were recorded by Christian monks in the 11th century, and many ancient Irish deities influenced the later canonization of Catholic saints, including St. Patrick and St. Brigid.

Irish tales were recorded by 11th-century Christian monks, which helped make Irish mythology the most well-preserved branch of Celtic mythology. In some parts of Ireland, there is still a belief in the Creideamh Sí, or fairy faith, that coexists with Catholicism.

What Is Irish Mythology?

Irish mythology is a branch of Celtic mythology which details the origin stories and deities, kings, and heroes of ancient Ireland. Celtic mythology encompasses the collections of Brittonic, Scottish, and Irish ancient beliefs and practices passed down by oral tradition. Among these, Irish mythology is the best preserved, owing to the Christian monks that entered the tales into the written historical record during the Middle Ages.

Ancient Irish myths are measured into four cycles. Each cycle details a group of pre-Christian deities, legendary heroes, or ancient kings, and the four cycles together chronologize the fabled settlement of the Emerald Isle.

  • Mythological Cycle: The first Irish mythological cycle details the arrival and disappearance of the first inhabitants of Ireland, a group of godlike or supernatural people called Tuatha Dé Dannan. The disappearance of these people gave rise to the Aos Sí, more contemporary mythical Irish creatures including leprechauns, changelings, and the Banshee. 
  • Ulster Cycle: The second cycle is thought to have taken place in the 1st century, around the time of the birth of Jesus Christ. It details quests and feats of ancient heroes, specifically in the areas of Ulster, in the north, and Leinster, in the east. 
  • Fenian Cycle: The third cycle recounts the journey of the hero Fionn mac Cumhaill and his mighty warriors, known as the Fianna. 
  • Historical Cycle: The final Irish mythological cycle, known as the Cycle of the Kings, is the history and genealogy of ancient Irish royals as told by court poets.

For centuries, Irish folklore passed through generations by oral tradition, though by the 11th century, they had been written down by monks. As a result, threads of Christianity are present in stories that would have had no notion of Christian faith. For example, the Mythological Cycle refers to the first settlers of Ireland as supernatural, godlike, or skilled in magic but never as gods, deities, or holy entities, though they would have been sacred to ancient people.

Irish Mythical Deities 

Ancient Irish mythological characters include venerated kings, heroes, and gods. The first cycle of Irish mythology, aptly known as the Mythological Cycle, is comprised of stories outlining the fabled founding of Ireland by the Tuatha Dé Dannan and, later, the Aos Sí.

The Tuatha Dé Dannan disappeared, giving rise to the Aos Sí, who existed in a parallel universe alongside venerated ancestors, ancient kings, and legendary heroes. This universe, called the Tir na nOg or the Otherworld, can be accessed on certain occasions at sacred places, including burial mounds, fairy hills, stone circles, and cairns. 

Tuatha Dé Dannan

According to legend, the Tuatha Dé Dannan, or “People of the goddess Danu,” were supernatural creatures with human forms that were skilled in magical arts. Their story is recorded in the Book of Invasions, one of the texts written by the 11th-century monks. The Book of Invasions detailed how the godlike people descended into Ireland with a thick fog that encompassed the land, and when the fog lifted, the Tuatha Dé Dannan remained.

When the Milesians, the ancient ancestors of the Irish people, arrived in Ireland, they conquered the land, and the Tuatha Dé Dannan disappeared. Some legends say they left Ireland completely and permanently, retreating to the Otherworld, while others say they blended together with the Milesians, passing some of the magic of the mythical deities into lives of the modern Irish people. Some of the most venerated figures of the Tuatha Dé Dannan include:

  • Dagda: God of life and death, patriarch
  • Lir: God of the sea 
  • Ogma: God of learning, creator of Ogham script
  • Lugh: God of sun and light 
  • Brighid: goddess of health and fertility 
  • Tree de Dana: Gods of crafts; Goibniu, the blacksmith, Credne, the goldsmith, and Luchtaine, the carpenter

Aos Sí

The Aos Sí, also known as the Sidhe (pronounced sith), are the “People of the Mounds” or the “Otherworldly Folk,” the contemporary depictions of the fairy folk. They are widely considered to be the descendants or manifestations of the Tuatha Dé Dannan who retreated the Otherworld, where they walk amongst human beings but generally tend to live separately from them. The common and contemporary Irish characterizations are rooted in the Aos Sí. Some of the most recognizable fairies are: 

  • Leprechaun: A solitary shoemaker known for causing mischief and keeping pots of gold.
  • The Banshee: Similar to the Latin American myth of La Llorona, the Banshee is a woman whose wailing signifies death. 
  • Changelings: A fairy child left in the place of a human child. Sick or disabled babies and children were often thought to be changelings, leading to devastating consequences until as recently as 1895, when Bridget Cleary was killed by her husband, who believed her to be a changeling.

The Aos Sí are known to inhabit places from which the Otherworld is accessible, including fairy hills, fairy rings, and notable geographical features like lakes, rivers, hills, and mountains. The Aos Sí are fiercely protective of their spaces, and they are known to seek vengeance on those who enter, intentionally or not.

Though the Aos Sí are mythical creatures, there is a strong sense of the Creideamh Sí, or Fairy Faith, cultivated by some Irish people. The purpose of Creideamh Sí, which coexists with Catholicism, is not necessarily worship, but rather the fostering of good relations. Followers of the Fairy Faith are conscious of sacred spaces, careful not to enter them or build over them. 

Christian Influence on Irish Mythology

The Christian monks and scholars who recorded ancient Irish myths did so with the bias of faith. As a result, Christian development and ancient mythology significantly influenced each other. For example, Ireland’s two patron saints, St. Patrick and St. Brigid, are rooted in ancient Irish mythology.

St. Patrick

The most glaring amalgamation of religious practices can be found in the annual celebration of St. Patrick’s Day, a holiday with Catholic roots that almost always features leprechauns in some capacity.

Contemporary holidays aside, early Christians in Ireland revered St. Patrick as a symbol of the triumph of Christianity over paganism. However, particularly in the same medieval texts that outline ancient Irish history, St. Patrick is not documented as a warrior, but rather as a mediator between Christian and Pagan cultures. 

St. Brigid

Most people who are familiar with Ireland recognize St. Brigid of Kildare as the second patron saint of the Emerald Isle, as well as the saint of a handful of other stations and vocations, including babies, midwives, Irish nuns, dairymaids. It is less commonly known that the story of St. Brigid is rooted in the legend of Brighid, one of the deities of the ancient Tuatha Dé Dannan. Brigid was the daughter of Dagda and the goddess of fertility and health, much like St. Brigid.


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Perkins, McKenzie. "Irish Mythology: History and Legacy." ThoughtCo, Aug. 28, 2020, Perkins, McKenzie. (2020, August 28). Irish Mythology: History and Legacy. Retrieved from Perkins, McKenzie. "Irish Mythology: History and Legacy." ThoughtCo. (accessed March 27, 2023).