Ancient Irish history and legends have come down to us through history thanks to the diligent chronicling of the early Christian monks. The best record of the rich Celtic mythological tradition is contained in the four cycles drawn up by twelfth century Christian scribes: the Mythological Cycle, the Ulster Cycle (also known as the Red Branch Cycle) and the Fenian or Fianna Cycle, and the Kings, or Historical Cycle.
Irish myths were probably recorded in the eighth century or earlier, possibly written by the Druids in Ogham. There are few surviving examples of Ogham because this writing was primarily done on bark, or or wands of hazel and aspen. However the legends of the early Celtic people were also passed down through the tradition of storytelling, and it was from this source that the Monks gathered their colorful tales.
The early medieval monks rewrote the oral stories in a style that was designed to be read aloud to noble or royal households. When they set themselves the task of constructing a pseudo-history of Ireland, they also recast the ancient myths and legends into a Christian mold. In doing so, they demoted the old gods to mortals, and rewrote the sagas into an almost indecipherable maze of conflicting events.
Fortunately, there are a number of manuscripts which have survived fairly intact, and there are many others not yet translated into English. The Lebor Gabála or "Book of Invasions" is one of a number of manuscripts from which our knowledge of Celtic pre-history is derived.
Ó hÓgáin gives an account of the Mythological Cycle, a collective term applied to the stories in Irish literature which describe the doings of otherworld characters. The central theme was concerned with the successive invasions of Ireland by supernatural clans. These series of invasions are described in the Lebor Gabála or Book of Invasions.
The early supernatural inhabitants of Ireland included the Partholonians, the Nemedians, the demonic Fomhóire and the Fir Bholg, the divine Tuatha Dé Danann, followed by the Milesians.
The Milesians, lead by the Sons of Mill, were the fictional but first human ancestors of the Irish people. They defeated the Tuatha Dé Danann at the battle of Tailtiu, after which Ireland was in their possession. They divided it into two parts, with Éireamhóin ruling in the north and Éibhear in the south.
The main occupation of the Fenian Cycle is hunting. The Fenians, or Fianna, were a legendary band of heroes who defended Ireland and Scotland and kept law and order. Their leader was the mythical Fionn mac Cumhaill.
Fionn mac Cumhaill was the truest, wisest and kindest of the Fianna. He had two sons, Fergus of the Sweet Speech and Ossian, who is credited with a series of poems known as the 'Ossianic Ballads'. Ossian went to the Land of Youth with Niamh. His mother was Sadb, who was changed into the shape of a deer by a druid.
The warrior Caoilte was Fionn's right hand man, and he is reputed (in the monks' retelling of the ancient tale,) to have extolled the virtues of the Fianna when conversing with St. Patrick in the 'Dialogue of the Elders'. Other notable Fenians include Oscar, the greatest warrior, Conan, Goll mac Morna, and Diarmait O'Duibhne, who eloped with Fionn's betrothed, Grania.
The tales of the Fianna are heroic and fantastic, incorporating much interaction with the gods.
A large body of heroic tales in Irish literature describe the activities of the Ulaidh, an ancient people from the whom the province of Ulster got its name. The central story in the cycle is called Táin Bó Cuailnge: The Cattle Raid of Cooley.
The Cattle-Raid of Cooley is the central epic of the Ulster cycle. The saga begins as Queen Medb of Connaught amasses a large army in order to gain possession of a magnificent bull belonging to Daire, a chieftain of Ulster. As the men of Ulster are afflicted by a debilitating curse, the seventeen-year-old Cuchulain must defend Ulster single-handedly. The battle between Cuchulain and his friend Ferdiad is one of the most famous passages in early Irish literature.
Cúchulainn was Ulster's greatest hero. His father was said to be the sun god Lugh, and he trained in arms under the formidable warrioress Scathach. His greatest deeds are told in the Tain.
The Kings Cycle, also known as the Historical Cycle, is a book of tales chronicling historical or semi-historical kings of Ireland, generally from early AD to the middle ages.
Around the 12th century, the tales and sagas of of Ireland were organized and classified according to the first words in their titles. The tales were then catagorized as either prem-sceil ("chief tales") or fo-sceil ("minor tales"). Several lists exist, and differ in their content, so the following is only a general compilation.