The subject of tribal genealogy upon which the whole social fabric depended was far too important to be left without a check in the hands of tribal historians, however well-intentioned. And this check was afforded by the great convention or Féis, which took place triennially at Tara,[8] whither the historians had to bring their books that under the scrutiny of the jealous eyes of rivals they might be purged of whatever could not be substantiated, "and neither law nor usage nor historic record was ever held as genuine until it had received such approval, and nothing that disagreed with the Roll of Tara could be respected as truth."[9] "It was," says Duald Mac Firbis[10]--himself the author of probably the greatest book of genealogies ever written, speaking about the chief tribal historians of Ireland, "obligatory on every one of them who followed it to purify the profession"; and he adds very significantly, "Along with these [historians] the judges of Banba [Ireland] used to be in like manner preserving the history, _for a man could not be a judge without being a historian_, and he is not a historian who is not a judge in the BRETHADH NIMHEDH,[11] that is the last book in the study of the Shanachies and of the judges themselves." The poets and historians "were obliged to be free from theft, and killing, and satirising, and adultery, and everything that would be a reproach to their learning." Mac Firbis, who was the last working historian of a great professional family, puts the matter nobly and well. "Any Shanachie," he says, "whether an ollav or the next in rank, or belonging to the order at all, who did not preserve these rules, lost half his income and his dignity according to law, and was subject to heavy penalties besides, so that it is not to be supposed that there is in the world a person who would not prefer to tell the truth, if he had no other reason than the fear of God and the loss of his dignity and his income: and it is not becoming to charge partiality upon these elected historians [of the nation]. However, if unworthy people did write falsehood, and attributed it to a historian, it might become a reproach to the order of historians if they were not on their guard, and did not look to see whether it was out of their prime books of authority that those writers obtained their knowledge. And that is what should be done by every one, both by the lay scholar and the professional historian--everything of which they have a suspicion, to look for it, and if they do not find it confirmed in good books, to note down its doubtfulness,[12] along with it, as I myself do to certain races hereafter in this book, and it is thus that the historians are freed from the errors of others, should these errors be attributed to _them_, which God forbid."