The History of Rome (1.18.10-1.19.4)

Then he described in the usual formula the augury which he desired should be sent. They were sent, and Numa being by them manifested to be king, came down from the “ templum.” [*]

Having[*] in this way obtained the crown, Numa prepared to found as it were anew by laws and customs that City which had so recently been founded by force of arms He saw that this was impossible whilst a state of war lasted, for war brutalised men.

Thinking that the ferocity of his subjects might be mitigated by the disuse of arms, he built the temple of Janus at the foot of the Aventine as an index of peace and war, to signify when it was open that the State was under arms, and when it was shut that all the surrounding nations were at peace.

Twice since Numa's reign has it been shut, once after the first Punic war in the consulship of T. Manlius, the second time, which heaven has allowed our generation to witness, after the battle of Actium, when peace on land and sea was secured by the emperor Caesar Augustus.

After forming treaties of alliance with all his neighbours and closing the temple of Janus, Numa turned his attention to domestic matters. The removal of all danger from without would induce his subjects to luxuriate in idleness, as they would be no longer restrained by the fear of an enemy or by military discipline. To prevent this, he strove to inculcate in their minds the fear of the gods, regarding this as the most powerful influence which could act upon an uncivilised and, in those ages, a barbarous people.