Other scholars trace the precedent for killing Christins to Nero. Barnes explains that, though there was no Roman law, there was "ample precedent for suppressing foreign superstitions" prior to Nero. Precedent was based on strong feeling that only the ancestral Gods ought to be worshipped. Such feeling could "acquire the force of law", since the ancestral customs – the "Mos maiorum" – were the most important source of Roman law. In Joseph Bryant's view, "Nero's mass executions ...set a precedent, and thereafter the mere fact of 'being a Christian' was sufficient for state officials to impose capital punishment". Barnes says "Keresztes, goes so far as to claim that 'there is today an almost general agreement that the Christians, under normal circumstances, were not tried on the basis of either the "ius coercitionis" [(the governor's 'power of arrest'), or the general criminal law, but on the basis of a special law introduced during Nero's rule, proscribing Christians as such". This theory gives great weight to Tertullian, and Nero's older resolution forbidding the introduction of new religions, and the even older Republican principle that it was a capital offense to introduce a new superstition without the authorization of the Roman state.