Roman emperors Honorius and Theodosius II issue a new law banning rebaptism of Christians. The law is aimed at Montanists who believe that Christians who had renounced their faith during anti-Christian persecutions need to now be rebaptized to be legitimate members of the Christian church.
Orthodox Christians had decided that these "lapsi," or lapsed Christians, don't need to be rebaptized and that their original baptisms remained valid.
This new Roman law states:
"No person shall resort to the crime of rebaptizing, nor shall he endeavor to pollute with the filth of profaned religions and the sordidness of heretics those initiated into orthodox rites.
... if any person should be discovered to have rebaptized anyone who had been initiated into the mysteries of the Catholic sect, he shall suffer the penalty of [death], along with the person rebaptized." [CTh 16.6.6]
Montanism, named after its founder Montanus, is generally orthodox in its beliefs but is condemned as heretical because it promotes a spontaneous worship style which relies upon visits from the Holy Spirit as well as a very conservative standard of personal morality. There are strong parallels between Montanism and modern-day Pentecostalism.