We analyze the principles guiding the exclusion of certain free inhabitants from the political communities in which they lived and often prospered, the initiatives taken by ancient states to integrate them despite their secondary rank, the non-citizens' own efforts at integration, and the evolution of these interactions over time. We also study the factors that influenced both exclusion and integration (ethnicity, religion, etc.) and how the broad and ever-changing spectrum of what we call 'non-citizens' provides us with a window into the formation/transformation of categorial infrastructures from the ancient to the medieval world.