In Roman history and legend, the Gates of Janus were opened when Rome went to war and shut when the whole Roman world was at peace. According to Livy 1.19 the second king of Rome, Numa Pompilius, decided to distract the early, warlike Romans from their violent ways by instilling in them awe and reverence. His projects included establishing religion, certain priesthoods, and the building of temples as a distraction with the beneficial side effect of imbuing superstition. Karl Marx was later inspired by this passage to coin the phrase "religion is the opiate of the masses." The Temple of Janus was Numa's most famous temple project. It was located in the Roman Forum near the Argelitum.
During Numa's reign, the Gates of the Temple of Janus were closed and Rome remained at peace. The next king, Tullus Hostilius, opened the Gates of Janus when he went to war with Alba Longa. The Gates of Janus remained open for the next 400 years until after the First Punic War when T. Manlius Torquatus closed the Gates of Janus in 235 BC. This closure lasted about eight years. War with the Gauls in Northern Italy forced the Gates of Janus to reopen. They did not close again until 29 BC, following the deaths of Antony and Cleopatra.
The emperor Augustus boasted in his autobiographical Res Gestae paragraph 13 that he closed the Gates of Janus three times. From Cassius Dio 51.20 and 53.27 we are able to date the first two closures to 29 and 25 BC respectively. Thus, Augustus closed the Gates of Janus more times than in all prior Roman history.
The exact date of the third closure remains a scholarly debate. The only ancient author to date the third closure was Orosius,[1] who associates the event with the birth of Christ, ca 1 BC. However, modern scholars almost universally reject Orosius because Roman armies were campaigning in Germany and/or the Far East elsewhere by 2 BC. Inez Scott Ryberg and Gaius Stern date the third closure to 13 BC based on the joint return of Augustus and Agrippa to Rome after pacifying the provinces.[2] Sir Ronald Syme [3] dated the closure to 7 BC, to coincide with the triumph of Tiberius and his second consulship, the events of which year are lost in a gap in the surviving manuscripts of Cassius Dio. Mario Torelli followed Orosius' date.[4]
Later emperors also closed the Gates of Janus to great fanfare. The most famous closures occurred under Nero and Vespasian. Nero minted a large series of coins with the Ara Pacis on the reverse to commemorate this event. Other emperors certainly closed and reopened the Gates of Janus, but references in later and less thorough historians are fairly rare.
The poet Virgil also includes in the Aeneid the opening of the Gates of Janus to start war between the Trojans and the Latins.[5]
Augustus Res Gestae 13.
Livy 1.19.
Vergil _Aeneid_ 7.601-22.
Velleius Paterculus 2.38.3.
Plutarch, Numa.