Mugdorna was a part of the Kingdom of Airgíalla, one of the major over kingdoms in medieval Ireland. Airgíalla was a confederacy of nine independent petty kingdoms who elected an overlord between them. In earlier times they were probably subject to the Ulaid until the Battle of Fochairt¹ in AD735. After this the Uí Néill asserted their dominance throughout the North and Airgíalla was reduced to a vassal kingdom.

The Mugdornai were based in south Monaghan but their territory also stretched into northern Meath, where they ruled from the crannóg on Moynagh Lough, Nobber.² Excavations of the crannóg indicate it was built prior to AD685³ over a much earlier site. In the Tripartite Life of St. Patrick, the ‘Huí Segain’ are mentioned as ruling nearby at Kilmainhamwood. These might be one of the Mugdorna septs known as ‘Mugdornai Seagain’,⁴ meaning the Mugdornai could have had a presence in the area as early as the 5th century.

Sometime between AD785-793 Mugdorna split in two.⁵ The branch in Brega took the name ‘Mugdorna Breg’ while their northern counterparts were called ‘Mugdorna Maighean’. Mugdorna Breg seemed to have considerable ecclesiastical influence in Meath and were affiliated with the churches of Slane, Donaghmore and Kilbrew.⁶ Around AD800, they were driven out of Brega by the Gailenga and pushed back into Monaghan. This setback seems to have been only temporary though, as they are recorded as defeating the Vikings in Brega in 836AD:

“A battle was gained by the men of Breagh over the foreigners in Mughdhorna Breagh; and six score of the foreigners were slain in that battle” ⁷

From the 9th century onwards Mugdorna Breg was aligned to the Southern Uí Néill, while Mugdorna Maighean remained under Northern Uí Néill influence. Later in the 9th century, another branch of Mugdornai came to power with the help of the Northern Uí Néill. These were called the Fir Rois and ruled around Carrickmacross. By supporting the Fir Rois, the Northern Uí Néill were attempting to create buffer zone between Ulster and Brega.⁸

Mugdorna Breg is last mentioned independently in 955AD⁹ and may have ceased to exist as a kingdom after this, or may have re-joined with the northern kingdom into a greater Mugdorna.

References

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1. Charles Doherty, ‘Airgialla’ in Sean Duffy (ed.) Medieval Ireland: An Encyclopedia (New York, 2005), pp. 13-14
2. Edel Bhreathnach, ‘Topographical note: Moynagh Lough, Nobber, Co. Meath’ in Ríocht na Midhe, 9.4 (1998), pp. 16-19
3. John Bradley, ‘Archaeological Excavations at Moynagh Lough, County Meath’ in The Journal of the Royal Society of Antiquities of Ireland, Vol. 121 (1991), p. 24
4. Pilip Ó Mórdha, ‘The Medieval Kingdom of Mugdorna’ in Clogher Record Vol. 7, No. 3 (1971/1972), p. 434
5. Ó Mórdha, ‘The Medieval Kingdom of Mugdorna’, pp. 437-438
6. Edel Bhreatnach, Ireland in the Medieval World AD400-1000 (Dublin, 2014), p. 47
7. John O’ Donovan, Annals of the Kingdom of Ireland by the Four Masters, from the earliest period to the year 1616, Vol. 1 (Dublin, 1848), p. 455
8. Dáibhí Ó Cróinín, A New History of Ireland: Prehistoric and Early Ireland (Oxford, 2005), p. 884
9. The Annals of Ulster, Year 955.2, Available at https://celt.ucc.ie (Feb. 1st, 2022)

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