Let it be noted that Cashel, the seat of the Munster kings in Christian times, stands outside of ancient Munster. Keating relates an ancient story telling how Cashel was "discovered" in the time of Corc, king of Munster, _i.e._, about A.D. 400, and got a new name. This new name was a Latin one, for Caiseal is the Irish representative of the Latin word _castellum_, "fortress." These things show how late was the use of Cashel as the seat of Munster sovereignty. What and whence was this new ruling power in Munster, the Eoghanachta? Their genealogies show that at one time they were worshippers of a god named Segomo--one of their ancestors is named Nia Segomon, "Segomo's champion." This god Segomo is unknown to Irish tradition, in which his name is never found outside of the Eoghanacht genealogy. He was known, however, and worshipped in Gaul, where he is commemorated in several inscriptions of the Roman period. He was a war-god and is equated, according to the fashion of Roman Gaul, with the Latin god Mars--"Deus Mars Segomo." The descendants of Segomo's Champion are named in three Ogham inscriptions, all found in the district of Dungarvan and Ardmore, on the southern seaboard. The indications therefore are that the Eoghanachta represent a relatively late Gaulish settlement in that part of Ireland. The story of the Déisi Migration mentions several bodies of Gaulish settlers. The Migration of the Déisi is an evident sequel of the conquest of Tara and eastern Meath under Cormac. Déisi means "vassal communities." These particular vassal communities dwelt around Tara, and were possibly identical with the Luaighni, who formed the chief fighting force of North Leinster in Cú Chulainn's time. They quarrelled with Cormac, we are told, and he drove them, or a large part of them, out of Meath. They migrated in two bodies. One body crossed the sea and settled in southern Wales where the descendants of their princes still held sway in the eighth century. The other body settled for a time in Leinster. Later on this Leinster section entered into an alliance with the Eoghanacht king, Oengus, whose queen was the daughter of their chief. By their aid, Oengus conquered what is now the south-eastern part of Munster, and he settled the Déisi as frontier colonists on the conquered territory. Oengus flourished in St. Patrick's time, the second and third quarter of the fifth century. The loss of the large territories about the Boyne and the Suir reduced Leinster to much smaller dimensions. What remained of the two ancient Fifths was now united in one kingdom, ruled over by the line of the ancient kings of South Leinster. This reduction and unification means the final passing away of the Pentarchy described in the Ulster tales. The seat of the Leinster kings is no longer either Tara or Dinn Riogh, but Ailinn, which lies between them, on the southern side of the Curragh of Kildare.