This dissertation comprises an examination of the criminalization and prosecution of religious sectarianism during the first century of the Roman Empire's Christian era (the seminal period of the crime of heresy). The antisectarian legislation issued during this period is analysed in order to deduce the concerns informing it. This analysis serves as a basis for an asessment of whether the nature of the antisectarian legislation validates the explanation currently offered by legal historians for the emperors' prosecution of sectarianism, which states that religious dissidence represented a manifestation of social and political discontent in an era when such discontent could not be expressed through more appropriate avenues, and that the antisectarian measures thus represented a reaction to a secular threat. The foregoing analysis is conducted in three stages. First, the context in which, and the process whereby sectarianism was criminalized, is set out. Secondly, the criminal prosecution of sectarianism is discussed, focusing in turn on the elements of liability, the procedure whereby liability was determined in a given case, and the punishments imposed on conviction. The above aspects are discussed in some detail; as no comprehensive legal analysis of the prosecution of sectarianism during the relevant period exists as yet, it is necessary to create a proper frame of reference for further assessment. Finally, the nature of the antisectarian measures is considered. It is determined that there are no explicit or implicit indications in the legislation supporting the thesis that the emperors perceived sectarianism as an expression of social revolt and suppressed it on that account. It is further determined that there are no indications validating a nationalist thesis: although some correspondences between the rules relating to the prosecution of sectarianism and of political offences exist, these relate to features encountered more generally in Roman criminal law and thus are not significant; furthermore, there are important differences in the prosecution of sectarianism, and suppression of politically dangerous conduct, which are of such a nature that they indicate that the emperors' concern in the former case, differed fundamentally from that which informed the latter. It is concluded that the nature of the antisectarian legislation does not validate the socio-political thesis now current among legal historians, but rather serves to confirm the emperors' statement that religious piety informed their antisectarian programme.