In his treatise How to write history Lucian states that «in his books» the historian should be «a foreigner and a man without a country, independent, subject to no sovereign». This statement is not a sophistic paradox. It comes from a long tradition
regarding Greek historians, which considers a biographical accident – the situation of exile – as a necessary condition for historical inquiry. This paper aims at reconstructing this tradition, from Herodotus to Arrian, and at showing it to be one of the most important paradigms of historical knowledge.