One of the commonest assumptions underlying the academic study of the Jewish communities of the Graeco-Roman world is the certainty of Jewish ethnic continuity in diaspora settings. Ancient Jews, according to this line of thought, were committed to an ancestral heritage that ensured their separation from non-Jews and, with a few minor exceptions, secured the continuity of Jewish existence even outside the Jewish homeland.1 This model, which is clearly based on the experiences of the mediaeval Jewish diaspora, often determines the ways in which the fragmentary evidence for the ancient Jewish diaspora is collected, analysed, and presented. The purpose of this chapter is to challenge this model, based as it is on a diachronic analysis of Jewish history, by positing an alternative model, based on a synchronic examination of the diasporic experiences of some of the Jews’ closest neighbours. Given the limitations of time and space, the examination of the evidence will be far from complete, and will focus mainly on the Jews of the Egyptian chora. But even this brief sketch should suffice to demonstrate that Jewish continuity in diaspora settings cannot be taken for granted, and that in some cases it may have been the exception, not the rule.