Following the destruction of Jerusalem in 70 CE and the imposition of a direct Roman rule over Palestine, the rabbis transformed the corpus of biblical commandments, Judean legal practices and customs into a comprehensive and detailed legal system. How can we explain the surprising fact that it was specifically under Roman jurisdiction that Jewish law emerged for the first time as a cohesive and codified system of civil law? In this article I argue that rather than functioning as an ideological or utopian construct, the creation of rabbinic law under Rome follows a familiar pattern well attested in the study of indigenous law under colonial rule. Scholars have recurrently described the development of local legal practices into fixed and formal legal systems, following colonial standards, thus triggering the invention of colonized “customary law”. In a similar manner, papyrological evidence attests to the crystallization of a corpus of “laws of the Egyptians” during the second century CE. Rabbinic material, however, offers the most detailed account of the processes by which the diversity of local customs characteristic of the pre-Roman period transformed into a fixed and general system of law at the hands of local experts. The article surveys three aspects of rabbinic legal innovation that feature elements of colonized “customary law”: the creation of new legal fields, codification of custom, and the establishment of a Roman-like court procedure. Together, these elements reflect the rabbinic effort to transform normative practices of different sources into a comprehensive legal system befitting imperial legal landscape.