Leinster is one of the four provinces of Ireland, in the southeast of Ireland. The modern province comprises the ancient Kingdoms of Meath, Leinster and Osraige, which existed during Gaelic Ireland. Following the 12th-century Norman invasion of Ireland, the historic "fifths" of Leinster and Meath gradually merged, mainly due to the impact of the Pale, which …Leinster is one of the four provinces of Ireland, in the southeast of Ireland. The modern province comprises the ancient Kingdoms of Meath, Leinster and Osraige, which existed during Gaelic Ireland. Following the 12th-century Norman invasion of Ireland, the historic "fifths" of Leinster and Meath gradually merged, mainly due to the impact of the Pale, which straddled both, thereby forming the present-day province of Leinster. The ancient kingdoms were shired into a number of counties for administrative and judicial purposes. In later centuries, local government legislation has prompted further sub-division of the historic counties.