The institutions of the Roman Republic (509-27 B.C.) were made to ensure, in theory, that electives and annuals magistracies must never be vacant. This fundamental juridical rule had as consequence an absolute continuity in the detention of the executive power which was based on ius, auspicia and imperium. However, it occurred several times that the supreme magistracies - consulate, military tribunate with consular power - were suspended because either of hindrance to the holding of consular elections or religious misgiving leading to ritual expiation and renouatio auspiciorum. The legitimacy and the legality of the solution to the vacancy of the executive power then relied on the patres auctores, holders of the auspicia patrum, exclusive privilege of the patrician senators. The venerable fathers, heirs of Rome's most illustrious families, were the only ones to be able to put an end to the vacancy of the magistracies by using the ritual called interregnum which appeared, according to the roman tradition, during the royal latine-sabine period and were connected to the famous myth of the dismemberment and the apotheosis of Romulus. The partition of the king's embodiment constitute, as such, a fundamental symbol of the representation of auctoritas patrum and of the republican magistracy of which it should be vain to search any historicity. The purpose of this study is thus to analyse the very old institution of the interregnum which, as many, was characterised by the progressive transformation from the sacred to the juridical. In every institutional system, the public law makes provision for exception recourses revealing the psychological representation of the sovereign power. Rome is not an exception to the rule; the city could even, in a certain manner, have invented it.