PARIS — It seemed like a good idea at the time, one for the annals of great publicity gimmicks. An ambitious Internet marketing company would sponsor a double-decker London bus to drive around central Paris, throwing cash from the windows in a promotional stunt.

But it didn’t quite work out as planned. Minutes before the event was to have started late Saturday morning, the police decided they did not like the look of the hard-jostling crowd of around 7,000 people that had formed near the Eiffel Tower in search of instant riches, and they ordered the event stopped before even a single centime had been handed out. Some in the crowd then ran amok.

In the ensuing mayhem, about a dozen people were arrested, store windows were broken, a car was overturned and at least one man was beaten by thugs. The riot police were called in to restore order.

Instead of the middle-class Parisians the organizers had hoped for, witnesses said the crowd, overwhelmingly young, male and poor, appeared to be made up mostly of residents of the tough suburbs that ring the French capital, as well as poor students and homeless men.