The word interrex, also known as inter-rex is from Latin, with which it was literally awarded to a ruler during the time of the Roman Empire or for its part to the Roman magistracy. The office or magistracy of interrex was supposedly created as a result of the death of the first king of Rome Romulus, and therefore its origin is obscured by legend. The Senate of the Roman Kingdom was unable to elect a new king. In order to continue with the government of the city, the Senate, which then consisted of a hundred members, was divided into ten decuriae, which means "groups of ten"; and from each of these decuriae a senator was nominated as decurio.
Each of the ten decurios in succession enjoyed royal power and their insignia for five days as interrex; and if no king was appointed at the expiration of fifty days, the rotation would begin again. During the period in which they exercised their power it was called an interregnum and at that time it lasted for a year, after which Numa Pompilius was chosen as the new king. After the death of each king after an interrex he was appointed by the Senate. The function of the interrex was to call a meeting of the Comitia Curiata to elect a new king.
The interreges were appointed under the Republic to hold the elections for the election of consuls when they, through civil commotions or other causes, such as death, had not been able to do so in their year in office. Each held the office for only five days, as under the kings. Elections were, as a rule, not held by the first interrex, which was originally the curio maximus; more generally by the second or third; but in one case it reads from an eleventh, and in another from an interrex XIV. The elections to elect the first consuls were in the hands of Sp. Lucrecio as interrex was also called Urbis prefect.
