Traditionally, Ireland was divided into two halves in common with many other societies. The boundary (prehistoric in origin) ran along the Eiscir Riada, a natural gravel ridge (laid down at the end of the last glaciation) running in a line roughly between Dublin and Galway. The cosmographic structure of Ireland is elaborated in the mythological literature, particularly in Lebor Gabala Erenn (The Book of the Taking of Ireland)—twelfth century in its present form but preserving materials going back to at least the eighth century. The earliest division in the remote past was said to be between the sons of Mil (immediate ancestor of the inhabitants of the island), Eremon and Eber. By the eighth century, however, the theory that was to endure throughout the historical period had emerged. The northern half was known as Leth Cuinn (Conn’s Half) and the southern half as Leth Moga (The Half of Mug). Conn (from whom the Connachta / Ui Neill) was the eponymous ancestor of the dynasties of the northern half. Mug or Mug Nuadat (the slave of Nuadu), also called Eogan, was the eponymous ancestor of the Eoganachta, the main dynasty of Munster. Since Conn means "head" or "chief" and mug means "slave," this also reflects the international pattern of binary opposition in such schemas. The theory of the two halves was elaborated in the eighth century and reflects the political equilibrium of that period with the Ui Neill dominating Tara in the northern half and the Eoganachta dominating Cashel in the southern half.
Leth Cuinn
Leth Cuinn, "Conn’s Half," the northern half of Ireland. The Connachta derive their name from Conn (Dal Cuinn, "Division of Conn") and from them is named the province of Connacht in the west of Ireland. The Uf Neill emerged from the Connachta as an independent group by the late seventh century. The Ulaid (Ulstermen), who would seem to have exercised over-lordship over the northern half in the protohistoric period, suffered massive defeats in the battles of Moira, County Down, in 637 and Faughart, County Louth, in 735. They never recovered. Their place was taken by the Cenel nEogain who gradually moved eastward across the Foyle from Inishowen and dominated all of the north by the mid ninth century, making the Air-gialla their vassals and dominating the Dal Riada of northeast Antrim, the Dal nAraide (Cruithin) of mid Antrim, the Dal Fiatach of Down, and many other groups that had formerly been under the Ulaid. In Connacht the Uf Briuin of County Roscommon came to dominate the province supplanting the Uf Fiachrach and Uf Maine, as well as a multitude of earlier populations. The southern Uf Neill had conquered the midlands from the Shannon to the sea absorbing many older population groups. The clan Cholmain became the dominant group among them. Both branches of the Uf Neill sought to dominate Leth Moga—indeed it was essential if they were to claim the high kingship— although major campaigns against Munster were rare before the eighth century. Although Leinster was within the cultural area of Leth Moga in the seventh century, by the eighth century it was dominated by the Uf Neill. Mael-Sechnaill mac Maele-Ruanaid, king of the southern Uf Neill, was the first high king with real power. He campaigned in Munster and was the first high king to reach the south coast in 858. The position of Osraige, lying between Leinster and Munster, was ambiguous, but in 859 it was alienated to Leth Cuinn. There were Munster challenges to the Uf Neill: Cathal mac Finguinne in the eighth century, Fedelmid mac Cremthainn in the ninth century, Cormac mac Cuilennain in the tenth century, and Brian Boruma in the late tenth century to early eleventh century. Of these Brian was the most successful. In the post-Viking period, the emergence of Dublin as an international trading port and the feudalization of Irish society brought about a gradual reorientation of politics in Ireland. The old pattern of north-south conflict was no longer as important as the competition to control the wealth of Dublin. Medieval kingdoms were emerging in both halves of the country, led by powerful families such as Ua Briain in Munster, Ua Conchobhair in Connacht, Mac Lochlainn and Ua Neill in Ulster, and Mac Murrough in Leinster. Many of the major battles of the twelfth century took place in the midlands with control of Dublin as the ultimate goal. As a result of this pressure, the Uf Neill kingdoms of the midlands were greatly weakened. The arrival of the Anglo-Normans in the late twelfth century was the final blow to the ancient divisions since they conquered and settled large areas in both halves of Ireland.
Leth Moga
Leth Moga, "Mug’s Half," "The Servant’s Half," from Mug Nuadat, "Servant of Nuadu," otherwise known as Eogan, eponymous ancestor of the Eoganachta, the main dynasty of Munster. The capital of Leth Moga was Caisel (Cashel in Tipperary), a borrowing of the Latin castellum (castle, fortress), and tradition claims that it was founded in the fifth century. This may be read against the background of Irish settlement within the borders of the Roman Empire in Wales and Cornwall. Cashel was distinct from other tribal capitals in that, despite underlying pagan elements, its foundation story ("The Finding of Cashel") is strongly Christian and many, but not all, of its kings were also clerics. The Eoganachta were spread throughout Munster—the main branches were the Eoganachta Aine, East Limerick; Eoganachta Glendamnach, North Cork; and the Eoganachta Chaisil, Tipperary. The kingship of Munster circulated among the various branches of the Eoganachta until it was virtually monopolized by the Eoganachta Chaisil from the mid ninth century onward. The wide settlement of the Eoganachta across Munster assured control of their many subject peoples. Several Munster kings campaigned against the Uf Neill. Cathal mac Finguine harassed the midlands and Leinster from 733 until 738, but although the Uf Neill accepted his strength within Munster, he was not allowed control of Leinster. Fedelmid mac Crimthainn, king (820-847) and abbot, provided a serious challenge to the Uf Neill invading the midlands and Connacht in the 830s and 840s. He was no respecter of churches sacking both Clonmacnois and Kildare, as well as many others. In 840, he camped at Tara, indicating his ambition to achieve political dominance, and became involved in Armagh politics toward the same end. He attempted to hold the Oenach Carman in 841 to demonstrate his overlordship of Leinster, but suffered a massive defeat. Cormac mac Cuilennain, king and bishop of Cashel (902-908) again attempted to win political supremacy, but was defeated at Belach Mugna in Leinster in 908. With Cormac’s death the power of the Eoganachta collapsed. Their place was taken by an obscure group that rose to power through their ability to control the portages on the lower Shannon—the Dal gCais. From them came Brian Borumha mac Cennetig (Brian Boru) who was arguably the first effective high king of Ireland from Munster. Brian dominated Munster and soon made his claim for the kingship of Ireland. His defeat at the battle of Clontarf beside the Norse town of Dublin highlights the reorientation of Irish politics at this time. By supplanting the Eoganachta as the traditional kings of Munster and the Ui Neill as the traditional occupants of the high-kingship, Brian introduced a new era in Irish politics. His descendants were to play a leading role in national affairs of the eleventh and twelfth centuries, controlling not only Dublin but also the Isle of Man for a period. They had international agreements and marriage alliances, corresponded with the Pope and Norman bishops—leading to the twelfth century church reform—and introduced Romanesque architecture. For them the concept of Leth Moga was no longer of major significance.
