There was one act that was not on the bill at Saturday’s Mumford & Sons outdoor music festival on the Eastern Promenade. It was the city of Portland itself.

“How many of you people are not from Portland?” banjo player Winston Marshall asked the crowd of more than 15,000, and what sounded like two-thirds screamed in assent. “How many of you are going to come back?” The roar said it all.

It is clear that Portland’s experiment in turning its magnificent East End park into a concert venue for a day was a success.The weather was perfect, the crowd well-behaved and local businesses got a boost from a parade of new customers.

But the greatest benefit may have been the positive exposure for the city itself to a crop mostly young people who will walk away from the event having had a very good time in a place where they may want to visit again, or even come to live.

In a state that is already boasts the oldest median age and is getting older, this kind of publicity can’t be bought.

If a band like Mumford & Sons wants to tell young people that Portland is cool, tip your top hat to them. Whether you like their music or not, that is good news.

There is enough credit to go around: The city had the right response and embraced the idea of an Eastern Prom concert with no hesitation. The band and the concert’s promoter, Lauren Wayne of the State Theatre, produced a daylong festival that engaged venues outside the chain-link fence set up for the event.

The crowd was invited to several official after-parties attended by band members at downtown nightclubs and encouraged to walk the streets and experience the city.

This not the norm for touring rock shows, where the acts forget what city they are in, get out as fast as they can and promoters have no interest in any other business than theirs making a dollar.

We don’t know if this was a one-of-a-kind event, or if it could be repeated with other bands in other years. There may be ways that future concerts could be better managed.

But Portland made the most of its time on the big stage Saturday, and everyone involved should take a bow.