Ara Pacis, the Augustan Altar of Peace.

Originally posted by Rob Shergold on Facebook/The Roman World, on 18 March 2018. 

This altar was dedicated by (Octavian) Caesar Augustus on 30 January, 9 BCE, five years after the quelling of 30 years of fighting that was sparked by the assasination of the divine Gaius Iulius Caesar on the 15 March, 44 BCE.  This existential crisis of the Roman Republic, however, started after Caesar conquered Gaul, in 49 BCE when the Senate ordered Caesar to relinquish his military command and Caesar crossed the Rubicon with his 13th Legion (lucky bastard!) instead, leaving his province and illegally entering Roman Italy under arms.  Civil peace was utterly destroyed as a result, and Caesar's victory in the fighting put him in place as Dictator, for him an unrivalled position of power and influence.

When the crisis was over with the Second Settlement in 23 BCE, the Roman Republic had mutated into an Empire.  The crisis had lasted twenty-six years.