In 534, Muirchertach died and was succeeded peacefully by Tuathal Maelgarb, another great-grandson of Niall. Contemporary with him, there was another of Niall's great-grandsons, Diarmait, whose father and grandfather had not reigned, and whose line therefore was in danger of exclusion from the monarchy. In 544, Tuathal was assassinated by a foster-brother of Diarmait, and Diarmait secured the monarchy. He is the last of the great-grandsons of Niall of whom we hear, and consequently the family of Niall ceases in his time to preserve its legal unity. From his death in 565 until the year 734, though the power and prestige acquired by the Ui Néill enabled them to keep the high-kingship among themselves, there is no regularity of succession. The Ui Néill held a number of small kingdoms in Meath and western Ulster, and whatever king of them showed himself to be the strongest is recognised as king of Ireland. The Northern Ui Néill, occupying a compact territory side by side, continued to hold together in political unity until the seventh century, their chief king being at one time of the line of Conall Gulban, at another time of the line of Eogan. In 563 they conquered from the Picts a belt of territory on the western side of the Bann, between Loch Neagh and the sea. This territory came into the possession of a branch of Eogan's line, represented in later times by the family of O'Catháin (O'Kane). In 615, we see the first appearance of a break in the unity of the Northern Ui Néill. Mael Chobo, of the line of Conall, was then their king and king of Ireland. He was overthrown in battle by Suibne Menn, king of Cenél Eogain, who then became king of Ireland. Thenceforward, Cenél Conaill and Cenél Eogain become rival powers in the North. Their rivalry lasted, with intervals, for a thousand years, until the battle of Kinsale in 1601, where it was a contributary cause of the final overthrow of both their houses. Cenél Eogain, from the position of its territory, held the advantage, and gradually extended its power eastward and southward over Ulster. Cenél Conaill on the other hand, holding the natural fastness of the Donegal Highlands, was never forced to take a permanently subordinate position.