Rome kicked off an all-night street party to celebrate the blocking of the main road to the Colosseum to private vehicles to protect the ailing monument.
Rome's new Mayor Ignazio Marino launched the all-night festival, which would see artistic shows, concerts and film projections in the city, expected to draw thousands of tourists.
"I think we have the world's best-known monument and that we have turned it into a traffic circle," said Marino of the monument that has been blackened by pollution and is in a poor state.
From 0300 GMT Saturday, cars, lorries and other private vehicles were barred from using the last trunk of the avenue Via dei Fori Imperiali, which links Piazza Venezia to the iconic Roman amphitheatre.
Traffic has been diverted to an adjacent road and only public transport will be allowed on the old route.
The decision was taken by Marino of the leftist Democratic Party, who would like eventually to make the Via dei Fori Imperiali a pedestrian area.
"I say it with respect, but between the interest of someone who can't stop in front of his newsagent in his car, and the protection of the Colosseum, I choose the latter," Marino said.
"It is the start of a dream, a great revolution for our city."
The number of visitors to the Colosseum, the biggest ancient Roman amphitheatre ever built, has increased from a million to around six million a year over the past decade, thanks mainly to the 2000 blockbuster film "Gladiator".
But it has also fallen into disrepair in recent years: bits of stone, blackened by pollution, have fallen off and some experts have voiced concern that the foundations are sinking, and the amphitheatre is starting to lean.
Long-delayed repairs to the 2,000-year-old monument, funded by Italian billionaire Diego Della Valle, are in the pipeline -- but problems with red tape mean they have yet to get off the ground.