When a man died, all the living members of the _derbfine_ to which he belonged became his heirs, and the inheritance, if capable of division, was divided among them in proportions fixed by law. Thus, if the deceased belonged to the third generation of the four which formed the _derbfine_, his heirs comprised all his grandfather's living descendants--_i.e._ his own children, his brothers and their children, and his uncles and their children and grandchildren. In each case, the _derbfine_ or group of heirs was ascertained by counting back to the great-grandfather of the youngest member and comprised all his descendants. Kingship was not divisible, though it was a heritable property. When a man became king, then all male members of his _derbfine_ became potential heirs to the kingship. Each member became capable of succession. For a man who thus came into the line of succession, there was a legal name--he was called _rigdamna_, "king-material," or in homely phrase, "the makings of a king." When a vacancy occurred, it was filled up by election from among those in this way qualified. A glance at the genealogical tree (p. 193) will show how this law of succession influenced the action of the principals in the battle of Ocha. Muirchertach, king of Ailech, as the annals show, was the most active and daring of the Irish princes in his time. But neither his father nor his grandfather had held the high-kingship. If he himself failed to secure it, then the whole branch of the Northern Ui Néill ceased to have any lawful claim to the monarchy. He did not belong to the same _derbfine_ as the reigning monarch Ailill Molt, but he was eligible to the monarchy because his great-grandfather, Niall, had held it. It was therefore his interest, and that of his kinsfolk in the north-west, to strike in, cut out the Connacht branch, and secure the potential succession for himself and his posterity. Not relying on his own power to effect this, he came to an understanding with Luguid, king of the Southern Ui Néill, who belonged to his own _derbfine_. From the sequel, we may judge that the price of Luguid's adhesion was immediate succession to the monarchy. He became king of Ireland after the battle of Ocha, and Muirchertach became king of Ireland after him. It is evident that this law of succession, a part of the ordinary law of inheritance, was, from the point of view of the public peace, a bad law. There were always branches of the ruling lines which, like the Northern Ui Néill in this instance, were on the point of falling outside of the group of eligibles; and the chiefs of these branches were always under the temptation to use violent measures, if they felt themselves strong enough, to retain the legal qualification in their own line.