The population of Leinster is 2,501,208 according to the 2006 census, making it the most populous province in the country.
The traditional arms of Leinster have a golden harp on a green background, which has become the basis of the provincial flag.
The Gaelic Kingdom of Leinster before 1171 changed its borders as the fortunes of Ireland's constant wars dictated. At the coming of Strongbow in 1169 the kingdom was considerably smaller than today's province.
The first part of the name Leinster derives from Laigin, the name of a major tribe that once inhabited the area. The latter part of the name derives either from the Irish tír or the Old Norse staðr, both of which translate as "land" or "territory".
The tribes of Leinster were united by Úgaine Mor (Hugony, the Great), who supposedly built the hill-fort of Dún Ailinne, near Kilcullen, County Kildare. He is a likely, but uncertain candidate as the first historical king of Laigin (Leinster) in the 7th century BC. The kingdom of Laigin was re-founded circa 175/185 AD following a period of civil wars in Ireland by the legendary Cathair Mor. Finn Mac Cool, or Fionn mac Cumhaill, was reputed to have built a stronghold at the Hill of Allen, on the edge of the Bog of Allen, which was then in Leinster.
In the 4th and 5th centuries, after Magnus Maximus left Britain with his legions and later as the Romans left entirely, there was a power vacuum which Leinstermen exploited. Colonists from Leinster settled in North Wales, specifically in Anglesey, Carnarvonshire and Denbighshire, and in places left their names. The Llŷn Peninsula is believed to derive its name from Laigin and Brecknockshire takes its name from Brychan, an Irish prince who settled and ruled there.
By the 8th century, the rulers of Laigin had split into two dynasties:
- Northern Leinster dynasty: Murchad mac Brain (d. 727), King of Uí Dúnlainge, and joint leader of the Laigin
- Southern Leinster dynasty: Áed mac Colggen (d. 738), King of Uí Cheinnselaig, and joint leader of the Laigin
After the death of the last Kildare-based King of Laigin, Murchad Mac Dunlainge in 1042, the kingship of Leinster reverted to the Uí Cheinnselaig sept based in the south east, now County Wexford. This southern dynasty gave all the later Kings of Leinster.
Dermot MacMurrough and Strongbow
In 1167, Dermot MacMurrough, King of Leinster was deprived of his kingdom by Rory O'Connor, High King of Ireland. To recover his kingdom, King Dermot sailed for Bristol and thence to Aquitaine to solicit help from Henry II of England. In 1166, Henry authorised his subjects to support Dermot’s cause, and eventually Dermot found a willing supporter in Richard de Clare, 2nd Earl of Pembroke, nicknamed "Strongbow", lord of much of South Wales. Strongbow agreed with King Dermot to raise an army and that in return for restoring the king, Strongbow would receive Aoife, Dermot's eldest daughter, in marriage and would be Dermot's successor as King of Leinster.
In 1169, Strongbow's army set sail from Pembrokeshire, led by Raymond Fitzgerald and swiftly seized Wexford, Waterford and Dublin in 1169-1170. De Clare married Aoife in 1169 and sailed for Ireland in Leinster August 1170. In May 1171, Dermot died, leaving the kingdom disputed between Richard de Clare and Dermot's son, Donal MacMurrough-Kavanagh. In the event, King Henry II settled the matter, dispossessing both and establishing himself in Ireland. The Kingdom of Leinster was at an end.
Under the new rulers, the ancient Kingdom of Meath and Leinster merged together. Ancient Meath is today much of the counties of Meath and Westmeath. Another change in the Middle Ages was to County Louth, which was formerly part of Ulster and now belongs to Leinster.
- Foster, R. F. The Oxford History of Ireland. Oxford University Press, Oxford & New York, 1992. ISBN 0-19-285271-X (references to Irish colony in North Wales, Lleyn Peninsula, page 6)
- Kings, Saints and Sagas, Alfred. P. Smyth, in Wicklow:History and Society, 1994. ISBN 798 0906602300
- Settlement patterns in the early historic kingdom of Leinster (seventh-mid twelfth centuries), Mark Clinton, in Seanchas:Studies in Early and Mediæval Irish Archaeology, History and Literature in Honour of Francis John Byrne, ed. Alfred P. Smyth, pp. 275–298, Four Courts Press, Dublin, 2000.
- Kings, the kingship of Leinster, and the regnal poems of "laidshenchas Laigen":a reflection of dynastic politics in Leinster, 650-1150, Edel Bhreathnach, Seanchas ...", pp. 299–312.