In 1993, when Philadelphia's downtown was hitting bottom, Ed Rendell launched a visionary revival strategy disguised as an arts initiative. First, create a Philadelphia version of Broadway by clustering cultural venues on South Broad Street. Then, pray that suburbanites and tourists would feel safe enough to venture there after dark and drop a wad on dinner and show tickets.

Twenty years on, as the organization that manages the Avenue of the Arts celebrates its accomplishments, South Broad Street between City Hall and Spruce Street is, indeed, a sparkling Great White Way, abuzz in the evenings with people rushing to events. And yet the original premise is outdated: Out-of-town visitors are no longer the key to the city's salvation.

The challenge today isn't to cajole suburbanites to come downtown for an evening; it's making the city more livable for the thousands of new residents who are putting down roots in Philadelphia's reviving neighborhoods. No one anticipated that population surge when the avenue was created.

Without a doubt, South Broad has come a long way from its pre-Avenue-of-the-Arts days when office buildings stood empty, prostitutes strutted near the corner of Lombard Street, and the gloomy husk of the Ridgeway Library served as the face of the city's decline.

The Avenue of the Arts was proposed by Paul Levy's Central Philadelphia Development Corp.  in 1990 as a way to clean up that mess, but it was Rendell who ran with the idea. Rendell's laser focus, Levy says, enabled him to attract the public and private cash necessary to bankroll a dozen arts-related projects and fund a major streetscape overhaul.

Glamorous new destinations like the Kimmel Center, which opened in 2001, helped rebrand the avenue as an entertainment district. Historic buildings were saved; that white-columned Ridgeway is now home to the Creative and Performing Arts High School. Developers responded by renovating their mothballed Class B offices and, ultimately, dotting the blocks south of Spruce with new, high-end apartments and restaurants.

But while the Avenue of the Arts has enjoyed a respectable run as the star of the city's revival efforts, other, more sustainable trends have pushed it off the marquee. The most important is the rediscovery of the city by the millennial generation, which has dramatically repopulated the ring of neighborhoods around Center City, places with names that would have drawn blank stares in 1993, like Newbold, Old Richmond, and Spruce Hill. And their residents aren't the people filling Kimmel's balconies.

Ever since New York carved Lincoln Center out of the decaying Hell's Kitchen neighborhood in the '60s, cities around the country dreamed of having their own arts district. But concentrating culture is an old strategy that has run its course, says John D. Landis, chairman of Penn's regional planning department.

What drives cities now are entrepreneurs and what he calls "the Brooklyn phenomenon." The city, he explains, is where people go to "consume urbanism." Jeremy Nowak, the former head of the William Penn Foundation, agrees: "We've moved on to other strategies."

Some argue the Avenue of the Arts created the conditions that made the millennial boom possible. "Maybe the avenue isn't 100 percent responsible, but it was the catalyst," Rendell told me. "It got suburbanites to come in the city and eat."

It is certainly true that the fear of the gritty city has lessened in the last two decades. But that seems more likely the result of a bundle of policies that helped the whole city to reset its image.

Attention to the so-called broken-windows crimes by Rendell and Levy was at least as important in making people feel comfortable downtown. Without the 10-year property-tax abatement as an incentive, it is hard to imagine that Philadelphia would have seen its entire stock of vacant, early-20th-century office buildings transformed into apartments, or the subsequent boom in infill housing.

And let's not discount the profound changes in American life over the last 20 years. At the exact moment that the millennials - a generation, incidentally, with no memory of the urban upheavals of the '60s and '70s - were coming of age, the Internet gave them the flexibility to live wherever they like and work from home.

Since the branding of the avenue, Philadelphia has become a more multipolar place. While Broad Street is still filled on the weekends with people seeking food and entertainment, so is 13th Street, the high-style restaurant row developed privately by the late Tony Goldman. The same is true of East Passyunk Avenue and the Northern Liberties hipster cluster at Girard and Frankford Avenues. And soon, the avenue will have to compete with the Fringe Festival on the Delaware Waterfront.

It's worth noting that most of the avenue's culture is produced by legacy institutions like the Philadelphia Orchestra and theater companies whose audiences are rapidly graying. The new residents of Graduate Hospital and South Kensington tend to seek their amusements in nontraditional venues like the Fringe, Johnny Brendas, and the aptly named Underground Arts. No wonder several avenue stalwarts are struggling financially.

There are indications that the Avenue of the Arts Inc. recognizes that it needs to stretch its appeal beyond its core audience. This summer's pop-up beer garden, organized by the Pennsylvania Horticultural Society on a vacant lot across from the Kimmel, drew millennials in droves to South Broad. Too bad, though, that the agency chose to celebrate its anniversary with a cocktail party this week for the city's clubby (and elderly) elite, rather than a true, Philly-style block party for the masses.

The avenue's future - like the rest of Philadelphia - rests on its growing residential population. Developer Carl Dranoff is completing his third building and has his eye on at least two other sites, including Spruce Street's southeast corner.

With Philadelphia's population on the rise, developers are scrambling to discover the next hot residential neighborhood. Who knows? It could be South Broad Street.