Celtic mythology is the collection of stories and beliefs from the Celtic people. Like other groups in Europe during the Iron Age, the Celts believed in many gods and goddesses. The myths of the Celtic people who lived on the European mainland, such as the Gauls and Celtiberians, were lost after the Romans conquered them, their languages faded, and they converted to Christianity. Only a few pieces of these myths remain in writings by ancient Greeks and Romans and in archaeological findings. Most Celtic myths that survive today come from the Insular Celtic peoples, including the Gaels of Ireland and Scotland and the Celtic Britons of western Britain and Brittany. These groups kept their stories alive through spoken traditions, which were later recorded by Christian writers during the Middle Ages. Irish mythology has the largest collection of written myths, followed by Welsh mythology.

In Irish mythology, a supernatural group called the Tuatha Dé Danann is thought to represent the main gods of Ireland. In Welsh stories, many characters are linked to either the Plant Dôn ("Children of Dôn") or the Plant Llŷr ("Children of Llŷr"). Some figures in Insular Celtic myths have similar names or roles to those in continental Celtic traditions, such as Irish Lugh and Welsh Lleu, who are related to the god Lugus, and others like Goibniu and Gofannon, who are connected to Gobannos. Similar connections exist between Macán and Mabon with Maponos. A common character in these myths is the sovereignty goddess, who symbolizes the land and gives a king the right to rule by marrying him. Another shared idea is the Otherworld, a magical realm where supernatural beings live, often visited by heroes in myths. Celtic mythology also influenced later stories about King Arthur.

Overview

At its peak, the Celtic world included much of western and central Europe. However, it did not have a single government, and there was no one central place that controlled culture or made it the same everywhere. Because of this, religious practices varied greatly among different Celtic groups, even though some symbols, like the god Lugh, appeared in many areas. More than 300 gods have been recorded, often linked to Roman gods. Most of these were local or tribal gods, and few were worshiped widely. Still, from what remains of Celtic myths, it seems there were more shared beliefs than people often think.

The roles and identities of these ancient gods can be understood by looking at their names, where their names were written, their images, the Roman gods they were compared to, and similar figures in later Celtic myths.

Celtic mythology is divided into different but connected groups, based on the types of Celtic languages:

• Ancient Celtic religion (mainly studied through archaeological finds, not written stories)
• Myths in Goidelic languages, mainly Irish myths (also found in Manx and Scottish myths) — including the Ulster Cycle, Fenian Cycle, and Cycles of the Kings
• Myths in Brittonic languages — Welsh, Cornish, and Breton myths

Historical sources

Because few written materials from ancient Gaulish have survived, it is believed that many Celtic writings were destroyed by the Romans. However, evidence shows that a written form of Gaulish was used, including Greek, Latin, and Old Italic alphabets. This is supported by religious objects with Gaulish inscriptions and the Coligny calendar. Julius Caesar noted that the Gauls were literate, but he also wrote that druids, their religious leaders, were not allowed to write down certain sacred religious texts (Caesar, Commentarii de Bello Gallico 6.14). He also mentioned that the Helvetii people had a written record of their population (Caesar, De Bello Gallico 1.29).

The Romans promoted the use of public inscriptions and reduced the influence of druids in areas they controlled. Most religious inscriptions found in Gaul (modern France and northern Italy), Britain, and other regions where Celtic languages were once spoken were created after the Roman conquest.

Early Gaels in Ireland and parts of Wales used the Ogham script to write short messages, mostly names. More advanced reading and writing skills were not introduced to Celtic regions not conquered by Rome until the arrival of Christianity. Many Gaelic myths were first written down by Christian monks, but these records often missed the original religious meanings of the stories.

Irish mythology

Irish mythology is the main part of Celtic mythology that has survived. It was first shared through stories during the time before written records existed. Later, during the early medieval period, Christian writers recorded many of these myths. They changed some parts to fit Christian beliefs.

These myths are usually grouped into different sets called "cycles." The Mythological Cycle, also known as the Cycle of the Gods, includes stories and poems about the god-like Túatha Dé Danann and other mythical groups. Many of the Túatha Dé are believed to represent Irish gods. They are often shown as kings, queens, druids, bards, warriors, heroes, healers, and craftsmen with magical abilities. Important figures in the Túatha Dé include The Dagda ("the great god"), who was likely the main god; The Morrígan ("the great queen" or "phantom queen"), a goddess linked to war, fate, and leadership; Lugh; Nuada; Aengus; Brigid; Manannán; Dian Cecht, the healer; and Goibniu, the smith, who was one of the Trí Dé Dána ("three gods of craft"). Their main enemies were the Fomorians (Fomoire), whom the Túatha Dé defeated in the Cath Maige Tuired ("Battle of Moytura"). Other important works in this cycle are the Lebor Gabála Érenn ("Book of Invasions"), a legendary history of Ireland, and the Aided Chlainne Lir ("Children of Lir").

The Ulster Cycle includes stories about the Ulaid, a group of people. It focuses on the mythical Ulster king Conchobar mac Nessa and his court at Emain Macha, the hero Cú Chulainn, and their conflicts with the Connachta and queen Medb. The most important and longest story in this cycle is the epic Táin Bó Cúailnge ("Cattle Raid of Cooley").

The Fianna Cycle tells the adventures of the hero Fionn and his warrior group, the Fianna. It includes the long story Acallam na Senórach ("Tales of the Elders").

The Kings' Cycle includes stories about historical and partly historical kings of Ireland, such as Buile Shuibhne ("The Madness of King Sweeny"), and tales about the origins of families and groups.

There are also myths that do not fit into any of these cycles. These include the echtrai stories, which describe journeys to the Otherworld (such as The Voyage of Bran), and the Dindsenchas ("lore of places"). Some written works have been lost, and many myths were likely never written down.

Welsh mythology

Important elements of British mythology are found in the Four Branches of the Mabinogi, especially in the names of characters such as Rhiannon, Teyrnon, and Brân the Blessed (Bendigeidfran, "Bran [Crow] the Blessed"). Other characters likely come from mythological traditions, and certain stories, like the appearance of Arawn, a king of the Otherworld who asks a human for help with his disputes, and the tale of a hero who can only be killed under seemingly conflicting conditions, are also found in Proto-Indo-European mythology. The children of Llŷr ("Sea," similar to the Irish word Ler) in the Second and Third Branches, and the children of Dôn (similar to the Irish Danu and earlier Indo-European traditions) in the Fourth Branch are important characters, but the stories themselves are not the main source of British mythology.

Other mythological names and references appear in Welsh stories and traditions, such as in the tale of Culhwch and Olwen, where characters like Mabon ap Modron ("Divine Son of the Divine Mother") are mentioned, and in the Welsh Triads. However, not enough is known about the background of British mythology to create a full story of creation or a clear group of British gods. While there are similarities with Irish myths, there may not have been a single, unified British mythological tradition. Regardless of its origins, the surviving stories were used effectively in important literary works that reflected the cultural values of Wales during the early and later Middle Ages.

Remnants of Gaulish and other mythology

The Celts also worshipped many gods, but not much is known about them except their names. Some writings from ancient times include small pieces of stories or myths that might be Celtic.

According to a Syrian writer named Lucian, a god named Ogmios was said to lead a group of men who were tied by their ears to his tongue. This was meant to show how powerful his words were.

A Roman poet named Lucan, who lived in the first century, wrote about gods named Taranis, Teutates, and Esus. However, there is little evidence from the Celts themselves that these gods were especially important.

Many art objects, coins, and altars may show scenes from forgotten myths. These include images of a god named Tarvos Trigaranus or a rider who looks like Jupiter sitting on top of a creature with snake-like legs called an Anguiped. The Gundestrup cauldron is also thought to have mythic meanings.

Along with names of gods found in dedications, there are also images of gods without known names. These include pictures of a god with three heads or faces, a god sitting with legs crossed, a god holding a snake, a god with a wheel, and a rider with a giant kneeling beside him. Some of these images have been found in peat bogs from the Late Bronze Age in Britain, showing that these symbols existed before the Romans arrived and were used across Celtic cultures. The way these images are spread shows they were likely connected to specific groups and shared from central places along trade routes. The image of the three-headed god is most common among the Belgae people, who lived near the Oise, Marne, and Moselle rivers. The image of a rider with a kneeling giant is found on both sides of the Rhine River. These examples suggest that different regions preferred certain common symbols.

The most famous description of Celtic gods in Gaul comes from Julius Caesar’s writings about his war in Gaul. In this, he lists five main gods worshipped in Gaul at that time, comparing them to Roman gods:

Mercury was the most honored god, and many images of him have been found. He was believed to be the creator of all arts, the helper of travelers and traders, and the most powerful force related to trade and wealth.

Next, the Gauls worshipped Apollo, Mars, Jupiter, and Minerva. Caesar described these gods as having roles similar to those of other cultures: Apollo helped cure illness, Minerva encouraged skill, Jupiter ruled the sky, and Mars influenced war. MacBain suggests that Apollo may be similar to the Irish god Lugh, Mercury to the Irish god Manannan mac Lir, Jupiter to the Irish god the Dagda, Mars to the Irish god Neit, and Minerva to the Irish god Brigit.

In addition to these five, Caesar mentions that the Gauls believed their ancestors came from a god he compared to Dis Pater, who may be the same as the Irish god Donn.