Ron Reno notes in discussion on Vitruvius at my Roman Architecture course:
“Poor Vitruvius- He devoted this whole book to Augustus, who was well known to appreciate and actually read such books…. and then wham! About a decade later Augustus plunks his most important single piece of architecture, the Temple of Mars Ultor, right in the middle of Rome. In Chapter 7 of Book 1 Vitruvius warns us very clearly not to place a temple dedicated to Mars or to Venus (both of whom are prominent in this temple) inside a city. They should be placed outside the city walls “so that venereal lust will not become a commonplace for the city’s adolescents and matriarchs. … And if the divinity of Mars is honored outside the city walls, there will not be armed conflict among citizens,” working rather to ensure that the walls serve only to defend the city.
So here we have it – the explanation for the violence of the Roman mob and the lack of morality that came to epitomize later Rome. If Augustus would have listened to Vitruvius all of those classic Hollywood movies would be so …. boring!”
Now we know!