A new home for the Roman Empire's most famous peace symbol was unveiled on Friday after a turbulent seven years of building, polemics and alterations.
"We are giving the Ara Pacis back to the citizens of Rome, at once an ancient and modern monument," said Rome Mayor Walter Veltroni, who has championed US architect Richard Meier's ultramodern showcase since his election as mayor five years ago.
Speaking on Rome's traditional 'birthday' - the 2,759th anniversary of its mythical foundation - the centre-left mayor promised work to "integrate" the building into its surroundings.
Meier said he was "delighted" to have finally completed the project - Rome's first piece of modern architecture since Fascist days - for "such a great, grand city". "I hope that the people who come here will get a sense of peace and serenity," he added.
Media crews from all over the world snapped away as Veltroni cut the ribbon, while in the background a group of rightwing National Alliance (AN) party protesters waved Italian and black flags.
The building has still to be completed with an indoor auditorium and a fountain, expected to be finished in a matter of months.
But it is already facing its latest threat, from the AN candidate to run Rome.
Gianni Alemanno wants to dismantle the building, put it in the Roman outskirts and replace it with something more like the simple, glass Fascist-era showcase it supplanted. Veltroni's camp has blasted Alemanno's "extremist" and "absurd" proposal.
But the cultural heritage body Italia Nostra came out with a fresh denunciation of the "inappropriate" work. Meier's design, the first piece of modern architecture in Rome's historic centre since Fascist days, has had to be changed several times since Meier won the contract in 1995 - six years before Veltroni's election. Earlier this year, in the latest change, Meier said he was happy to put a piece of old Rome into the ultramodern site - a move some saw as a sop to critics. Meier was also "delighted" with Veltroni's announcement of an international competition for projects to integrate the Ara Pacis with the surrounding square.
The final version of the building has a museum, auditorium, restaurant, bar, 300-seater theatre and underpass leading to the Tiber.
To give old-style 'distinction' to the site, Meier has also added a grand travertine entrance stairway and a Roman-style monolith pointing towards Augustus's ancient Roman 'meridian', the point in the old Camp of Mars - now near the premier's office - where legions had to lay down arms if they were to be allowed into the city.
A recipient of architecture's prime laurel, the Pritzker Prize, in 1985, Meier has been mentioned in the same breath as Britain's Norman Foster and Italy's Renzo Piano, the high priests of modernism. His credits include the Getty Center in Los Angeles, Barcelona's Museum of Contemporary Art and Frankfurt's Museum of the Arts.
The altar was commissioned in 13 BCE to celebrate peace throughout the Roman Empire.
It was completed in 9 BCE, 23 years before Augustus's death at the age of 76 in 14 CE (AD).
The architectural hub of Ancient Rome, circled by a bas relief of a procession of peace showing Aeneas, the Earth, Italy and Rome, it marked the first emperor's victorious return from Spain and Gaul and celebrated the peace he had restored to the empire.
According to a tradition launched by Roman writers, Rome was founded by Romulus, a descendant of the Trojan hero Aeneas, in 753 BCE.
