This policy of the law in protecting masters from the evidence of their tortured slaves varied at different periods. From an expression of Tacitus, it would seem not to have been part of the original jurisprudence of the Republic, but to have arisen from a special decree of the Senate. In the early days of the Empire, while the monarch still endeavored to veil his irresponsible power under the forms of law, and showed his reverence for ancient rights by evading them rather than by boldly subverting them, Tiberius, in prosecuting Libo and Silanus, caused their slaves to be transferred to the public prosecutor, and was thus able to gratify his vengeance legally by extorting the required evidence.[1424] Subsequent emperors were not reduced to these subterfuges, for the principle became established that in cases of _majestas_, even as the freeman was liable to torture, so his slaves could be tortured to convict him;[1425] and as if to show how utterly superfluous was the cunning of Tiberius, the respect towards the master in ordinary affairs was carried to that point that no slave could be tortured against a former owner with regard to matters which had occurred during his ownership.[1426] On the other hand, according to Ulpian, Trajan decided that when the confession of a guilty slave under torture implicated his master, the evidence could be used against the master, and this, again, was revoked by subsequent constitutions.[1427] Indeed, it became a settled principle of law to reject all incriminations of accomplices. Having thus broken down the protection of the citizen against the evidence of his slaves in accusations of treason, it was not difficult to extend the liability to other special crimes. Accordingly we find that, in 197, Septimius Severus specified adultery, fraudulent assessment, and crimes against the state as cases in which the evidence of slaves against their masters was admissible.[1428] The provision respecting adultery was repeated by Caracalla in 214, and afterwards by Maximus,[1429] and the same rule was also held to be good in cases of incest.[1430] It is probable that this increasing tendency alarmed the citizens of Rome, and that they clamored for a restitution of their immunities, for, when Tacitus was elected emperor, in 275, he endeavored to propitiate public favor by proposing a law to forbid the testimony of slaves against their masters except in cases of _majestas_.[1431] No trace of such a law, however, is found in the imperial jurisprudence, and the collections of Justinian show that the previous regulations were in full force in the sixth century.