The total population of Ireland, when the Normans first entered it, can only be approximated by conjecture. Supposing the whole force with which Roderick and his allies invested the Normans in Dublin, to be, as stated by a cotemporary writer, some 50,000 men, and that that force included one-fourth of all the men of the military age in the country; and further, supposing the men of military age to bear the proportion of one-fifth to the whole number of inhabitants, this would give a total population of about one million. Even this conjecture is to be taken with great diffidence and distrust, but, for the sake of clearness, it is set down as a possible Irish census, towards the close of the twelfth century. This population was divided into two great classes, the _Saer-Clanna_, or free tribes, chiefly, if not exclusively, of Milesian race; and the _Daer-Clanna_, or unfree tribes, consisting of the descendants of the subjugated older races, or of clans once free, reduced to servitude by the sword, or of the posterity of foreign mercenary soldiers. Of the free clans, the most illustrious were those of whose Princes we have traced the record—the descendants of Nial in Ulster and Meath, of Cathaeir More in Leinster, of Oliold in Munster, and of Eochaid in Connaught. An arbitrary division once limited the free clans to six in the southern half-kingdom, and six in the north; and the unfree also to six. But Geoffrey Keating, whose love of truth was quite as strong as his credulity in ancient legends—and that is saying much—disclaimed that classification, and collected his genealogies from principal heads—branching out into three families of tribes, descended from Eber Finn, one from Ir, and four from Eremhon, sons of Milesians of Spain; and ninth tribe sprung from Ith, granduncle to the sons of Milesius. The principal Eberian families' names were McCarthy, O'Sullivan, O'Mahony, O'Donovan, O'Brien, O'Dea, O'Quin, McMahon (of Clare), McNamara, O'Carroll (of Ely), and O'Gara; the Irian families were Magennis, O'Farrall, and O'Conor (of Kerry); the posterity of Eremhon branched out into the O'Neils, O'Donnells, O'Dohertys, O'Gallahers, O'Boyles, McGeoghegans, O'Conors (of Connaught), O'Flahertys, O'Heynes, O'Shaughnessys, O'Clerys, O'Dowdas, McDonalds (of Antrim), O'Kellys, Maguires, Kavanaghs, Fitzpatricks, O'Dwyers, and O'Conors (of Offally). The chief families of Ithian origin were the O'Driscolls, O'Learys, Coffeys, and Clancys. Out of the greater tribes many subdivisions arose from time to time, when new names were coined for some intermediate ancestor; but the farther enumeration of these may be conveniently dispensed with.