Founding a colony, during the Roman Republic, was a longer and more complex pragmatic procedure than we could believe when reading, for instance, that Ariminum was “founded” in 268. Modern languages make no real distinction between the foundation of the city as an urban creation, and the institutional constitution of a political community, whereas the Latin vocabulary makes several nuances. “Founding”, in a modern meaning, doesn’t exist in Latin. The Romans made a clear distinction between urbem/oppidum condere and coloniam deducere, two verbs which are far from being synonymous. Another difficulty is the important difference between the Greek and the Roman ways of colonisation, and the related lexical differences. For instance, there is no Greek word to translate deducere. We will have to question the classical concepts deriving from an old prejudice according to which colonies were replicas of Rome, “founded” according to the Varronian sulcus primigenius ritual. The sources, even if relatively scares, show that a city destined for the establishment of a colony had to be “founded” only if it doesn’t already exist as a city or if it has been ritually destroyed. Oppidum condere (which we could translate as “founding a town”) was not the most important operation in the colonial procedure. Founding a new town may as well have been part of the consulare imperium, as we have examples of towns founded by magistrates without any popular vote or senate’s advice, and without any deductio. The most important act was in fact the deductio, which came as the conclusion of a one to two years procedure, and which was considered as the date of the beginning of the colony’s existence, even if not yet an independent city. Confronting the analysis of the foundation stages with the famous inscriptions of Aquilea and Vrso makes it possible to understand why two more years were necessary to gain a real political autonomy, and to show how one became citizen of a colony. Some institutional solutions were possible to reinforce a colony which needed more citizens but was incolumen, because it was then condita and it was then forbidden to “found” it again