A mythology developed that Labraid Loingsech had horses ears: he spent some time exiled in Transalpine Gaul (dated roughly to the period of the Roman–Gallic wars) where his grandmother was from and returned to Ireland with Gaullish mercenaries.

He established a base in the area, which was renamed from "Gailian" to Leinster, in reference to the pointed-spears held by the Gaullish Gaesatae mercenaries who provided the backbone of Labraid Loingsech's powerbase and brought him to the High Kingship.

By the time of Early Christian Ireland, the Laighín had lost their grip on Irish hegemony with the rise of the descendants of Conn of the Hundred Battles (the Connachta and the Uí Néill).

In the 9th century, the Laighín also regained control of Osraige but it remained a largely independent realm under the Mac Giolla Phádrag, from the semi-autonomous Uí Failghe kinship group.

Throughout the centuries after the Norman invasion, several Kings and also leaders from dynasties who had previously held the Kingship of Leinster, continued to resist the invasion and hounded the English Pale periodically from the Wicklow Mountains: including the leaders of the O'Toole and O'Byrne clans (notable examples include Art Óg Mac Murchadha Caomhánach and Fiach McHugh O'Byrne) until the 17th century.