There is no evidence that the Romans spoke of Judaism as a religio licita and arguments sometimes raised that an edict of Caesar granted Judaism this status is by no means accepted by all. This argument is based on the account of the Jewish historian Josephus in his Antiquities (14.211-28) but nothing there amounts to granting Judaism the status of religio licita. Both Rajak and Leonard Victor Rutgers address the problematic nature of Josephus' evidence.
Rutgers argues that the Roman state had no "Jewish policy." The various edicts listed by Josephus were local, ad hoc rulings by Roman magistrates formulated in response to particular incidents and situations as they arose. It is important to note that these edicts of toleration were not general and empire wide, but seem to have been issued on a city by city basis. Though these senatus consulta were ad hoc in nature, they also served as legal precedents to which future governors and emperors could appeal.
There is no evidence at all for the claim often made that under the emperor Domitian (reigned 81-96 CE) Christianity became a religio illicita; in fact, it would be strange if Domitian could have made such a ruling since the term did not yet exist and as noted, was not used officially. From the evidence it is far from clear that Domitian was even aware of Christianity as a group distinct from Judaism, much less persecuted its adherents. J.E.A. Crake observes that "It cannot be said that there is a very clear picture of Domitian's attitude toward Christians. Christian writers have picked him out as hostile, but they seem a little uncertain why he merited this distinction.
The evidence against Domitian derives largely from Eusebius, who preserves in his Ecclesiastical History what purports to be a portion of a work by Melito of Sardis, who died ca. 180 and who was supposed to have been bishop of that city. Only fragments of his work remain and most of it comes to us (as with so many other early Christian writings) by way of Eusebius. This document, entitled Petition to Antoninus, refers to persecutions by Domitian: "Of all the emperors, the only ones ever persuaded by malicious advisers to misrepresent our doctrine were Nero and Domitian, who were the source of the unreasonable custom of laying false information against the Christians" (Eusebius, Ecclesiastical History 4.26). But as T.D. Barnes notes “All other authors who depict Domitian as a persecutor derive their information directly or indirectly from Melito. This dependence nullifies their testimony. For Melito himself had no precise evidence: he employed (or invented) the story of persecution by Domitian to justify his argument that only bad emperors condemned Christians.” Even W.H.C. Frend, who says that "Domitian was not a man to tolerate religious deviations", cannot summon up much enthusiasm for a Domitianic persecution, concluding that "the persecution of Domitian does not appear to have amounted to very much.
As Crake concludes, "As most scholars recently have argued, there was no law, either existing section of criminal law, or special legislation directed against the Christians, under which Christians were prosecuted in the first two centuries" and that "there is little evidence to support the notion of Domitian as a prosecutor of Christians and T.D. Barnes agrees, going on to observe that "It would be a mistake to assume that there was a single Roman policy towards foreign cults which was unambiguous and unchanging - or even that Roman law provided unequivocal guidance on the subject.
It is therefore incorrect to speak of any official Roman designation of a religion being religio licita as such a designation implies an official policy that cannot be shown to have existed. The Roman government did not interfere with the ancestral customs and traditions of the various ethnic groups under its rule if they did not pose a threat to the state; and if Judaism was tolerated it was because in general, all religions (as indistinguishable from culture and ethnicity) were tolerated. Rutgers argues that "Roman magistrates treated the Jews the way they did not because they were consciously tolerant, but simply because they had no reason to hinder the free exercise of Jewish religious practices. There was, in effect, no rational basis for an edict declaring Judaism to be religio licita or for Christianity to be designated as a religio illicita; it would have been unnecessary in a world where while frowned upon, superstition (superstitio) which is how many Romans saw Judaism and Christianity, was not illegal.