With this exception, therefore, in its relations to the community, each family in the barbaric tribes was a unit, both for attack and defence, whether recourse was had to the jealously preserved right of private warfare, or whether the injured parties contented themselves with the more peaceful processes of the _mallum_ or _althing_. This solidarity of the kindred is the key to much that would otherwise appear irrational in their legislation, and left, as we have seen, its traces late in the customary law. CHAPTER II. THE OATH AND ITS ACCESSORIES. Between the commission of an offence and its proof in a court of justice there lies a wide field for the exercise or perversion of human ingenuity. The subject of evidence is one which has taxed man’s reasoning powers to the utmost; and the subtle distinctions of the Roman law, with its _probatio_, _præsumptio juris_, _præsumptio juris tantum_: the endless refinements of the glossators, rating evidence in its different grades, as _probatio optima_, _evidentissima_, _apertissima_, _legitima_, _sufficiens_, _indubitata_, _dilucida_, _liquida_, _evidens_, _perspicua_, and _semiplena_; and the artificial rules of the common law, so repugnant frequently to human common sense, all alike show the importance of the subject, and its supreme difficulty. The semi-barbarian, impatient of such expenditure of logic, arrived at results by a shorter process. The time has passed for the romantic school of writers who assume that the unsupported oath of the accused was originally sufficient to clear him of a charge, when the fierce warrior disdained to shrink from the consequences of his act. It was not, indeed, until long after the Teutonic tribes had declined from the assumed virtues of their native forests, that an unsupported oath was receivable as evidence, and the introduction of such a custom may be traced to the influence of the Roman law, in which the importance of the oath was overwhelming.[28] The Wisigoths, who moulded their laws on the Roman jurisprudence, were the only race of barbarians who permitted the accused, in the absence of definite testimony, to escape on his single oath,[29] and this exception only tends to prove the rule, for at the council of Valence, in 855, the Wisigothic custom was denounced in the strongest terms as an incentive to perjury.[30] It is true that the oath of a master could clear a slave accused of certain crimes,[31] which was no less an incentive to perjury, for the master was liable in case of conviction, but presumably in such case he took upon himself the responsibility and laid himself open to an accusation of perjury. As a rule, however, we may assume that the purgatorial power of a single oath was an innovation introduced by the church, which was trained in the Roman institutions and claimed for its members the privilege, when testimony was deficient, of clearing themselves by appealing in this manner to