Under the empire the system degenerated into an abuse, which reached its height during the reign of Tiberius, although the delators continued to exercise their activity till the reign of Theodosius. They were drawn from all classes of society,--patricians, knights, freedmen, slaves, philosophers, literary men, and, above all, lawyers. The objects of their attacks were the wealthy, all possible rivals of the emperor, and those whose conduct implied a reproach against the imperial mode of life. Special opportunities were afforded by the law of majestas, which (originally directed against attacks on the ruler by word or deed) came to include all kinds of accusations with which it really had nothing to do; indeed, according to Tacitus, a charge of treason was regularly added to all criminal charges. The chief motive for these accusations was no doubt the desire of amassing wealth, since by the law of majestas one-fourth of the goods of the accused, even if he committed suicide in order to avoid confiscation (which was always carried out in the case of those condemned to capital punishment), was assured to the accuser (who was hence called quadruplator). Pliny and Martial mention instances of enormous fortunes amassed by those who carried on this hateful calling. But it was not without its dangers. If the delator lost his case or refused to carry it through, he was liable to the same penalties as the accused; he was exposed to the risk of vengeance at the hands of the proscribed in the event of their return, or of their relatives; while emperors like Tiberius would have no scruples about banishing or putting out of the way those of his creatures for whom he had no further use, and who might have proved dangerous to himself. Under the better emperors a reaction set in, and the severest penalties were inflicted upon the delators. Titus drove into exile or reduced to slavery those who had served Nero, after they had first been flogged in the amphitheatre. The abuse naturally reappeared under a man like Domitian; the delators, with whom Vespasian had not interfered, although he had abolished trials for majestas, were again banished by Trajan, and threatened with capital punishment in an edict of Constantine; but, as has been said, the evil, which was an almost necessary accompaniment of autocracy, lasted till the end of the 4th century.
See Mayor's note on Juvenal iv. 48 for ancient authorities; C Merivale, Hist. of the Romans under the Empire, chap. 44; W Rein, Criminalrecht der Römer (1842); T Mommsen, Romisches Strafrecht (1899); Kleinfeller in Pauly-Wissowa?s Realencyclopädie.