Paris, with its historic buildings blackened by exhaust fumes, is going car-less for a day.
Paris Mayor Anne Hidalgo presided over Sunday's "day without cars," two months before the city hosts the global summit on climate change.
Mayors from Sao Paulo, Brazil, Brussels and Bristol were in Paris for the kick-off on the Champs-Elysees Avenue.
The avenue, normally congested with vehicles, is not the only sector of Paris having a car-less moment. Vehicles, including motorised bicycles, are forbidden in a quarter of the French capital and "strongly not recommended" throughout. Those who hit the road anyway must observe a 20 kilometre-per-hour (12.5 mph) speed limit.
However buses, ambulances, police vehicles, fire engines and taxis were allowed on the streets.