A study of the lexicon used in the Roman epigraphic treaties preserved in their original Latin version or in their Greek translation shows that the authors of these documents, as well as those responsible for their official translation into Greek, used various terms bearing on the religious dimension (ὅρκοι/foedus), the juridical form (συνθῆκαι/leges) or the content of the agreements (συμμαχία/societas). These differences can be explained by the changing function of the foedus. Initially conceived as a legal instrument to establish the terms of a military alliance between the Roman people and other communities, it later became a tool to guarantee the rights of the allies and to bestow privileges on them, while celebrating the maiestas populi Romani and the fides Romana.