The Ecloga restructured Justinianic law with modifications but omitted most provisions concerning eunuchs. Meanwhile, it introduced new forms of penal mutilation, notably replacing the death penalty in certain cases. Of particular relevance is E. 17.39, which prescribes kaulokopēsis (cutting off the penis) for those convicted of bestiality. Although this term’s precise anatomical scope is unclear, it clearly refers to a form of genital mutilation, potentially distinct from traditional castration (i.e. removal of testicles), the standard method for creating eunuchs in Byzantium. The Isaurian emperors rarely addressed eunuchs in law, resulting in limited scholarly attention being paid to their legal treatment during this period. Nonetheless, the emergence of genital mutilation as legal penalty in the Ecloga warrants analysis, particularly in the broader context of penal reforms involving bodily mutilation—such as the removal of the tongue, hand, nose, and genitals. This chapter examines the legal and historical contexts of such punishments, with an emphasis on genital mutilation, tracing its development primarily from Justinian’s reign through Christian influences and imperial ideology. In focusing on E. 17.39, it then explores the evolving conception of penal mutilation of male genitals against bestiality and its backgrounds from multiple perspectives.