Numa Pompilius

According to tradition, after the death of Romulus, there was an interregnum of a year, during which the senators ruled until the election of a Sabine king Numa Pompilius, who ruled for 43 years, from 715 to 672 b.C.
It was a period of peace. Instead of fighting against the nearby people, he devoted himself to teaching the Roman people religion and virtue. For this reason he erected temples and altars, created priests orders and also established all the religious cerimonies. It seems that he was the one who reformed the calendar.