Growing cities are ambitious cities. When newcomers were pouring into Philadelphia in the early 20th century, the city went on a municipal building spree, erecting many of the schools, clinics, rec centers, and police stations that we cherish today. It launched a similar campaign after World War II, one that gave us an extraordinary collection of Modernist structures. But when people and jobs fled to the suburbs in the 1970s, Philadelphia’s ambition withered.

Philadelphia has made a remarkable comeback over the last two decades, with 13 straight years of population growth. Yet, when it comes to civic buildings, it still behaves as if it were a city in decline.

The Kenney administration’s Rebuild initiative is a good first step at reversing that mind-set. But if you strip away the hype, it’s just a fancy way of branding a deferred maintenance program for libraries and rec centers. Meanwhile, many of the big civic projects that have gotten off the ground in last decade — the new Police Headquarters on North Broad, the branch library on South Broad, Family Court on Arch Street — have been outsourced to private developers, with mixed results.

Philadelphia has chosen to take the privatization route once again with a new firehouse project in South Philadelphia. The Department of Public Property is finalizing a deal that would give Alterra Property Group the right to redevelop the better part of the block across from Columbus Square in South Philadelphia. In exchange, Alterra would replace the existing firehouse at 12th and Reed with a new facility.

There’s no doubt that Alterra’s proposal contains many smart ideas. After all, it’s based on a version outlined in the city’s 2015 District Plan for South Philadelphia. But the deal being negotiated with the developer reveals just how limited the city’s architectural ambitions have become.

That simple Modernist firehouse was one of 22 similar structures produced between 1950 and the mid-'60s. It was a time of immense upheaval, yet the city was intent on bringing its municipal buildings into the modern age with style and flair. For decades, the firehouse gazed at another product of that idealistic era: a circular stone park pavilion designed by Roth & Fleisher, one of the city’s first women-owned architectural firms.

That beloved landmark was demolished this winter by the Department of Parks and Recreation. What are the chances that the new firehouse will be as good as either one of those humble midcentury gems?

I’m not arguing that the firehouse should be preserved — unlike the pavilion, which was truly unique. Opened in 1964, the low-slung building, home to the Engine 10 and Ladder 11 companies, isn’t the best among those Midcentury firehouses. Nor does it function very well, Fire Department Commissioner Adam K. Thiel told me. It’s too small to accommodate the decontamination rooms that firefighters now require after putting out blazes in homes filled with toxin-emitting synthetic materials. The building lacks showers and bathrooms for female firefighters, whose numbers are on the rise.

It’s also a waste of a terrific piece of real estate. The neighborhood around Columbus Square is growing rapidly, and the park is about to get a major face-lift. Under its proposal, Alterra would erect a midrise apartment building on the firehouse site, overlooking the square. That would give Columbus Square’s eastern edge the gracious residential ensemble it deserves.

Moving the firehouse makes sense, too. Because it would be located next to the police station at 11th and Reed — a small, underappreciated midcentury building designed by a disciple of Le Corbusier — the pairing would create a compact municipal cluster. Alterra has also promised to renovate a city-owned maintenance facility on Reed Street. It would turn the handsome, early 20th century loft building into a space for coworking and events, further enlivening the square.

Because these sorts of public-private partnerships are now so routine, we hardly stop to consider the trade-offs when the city inks a deal with a developer. The obvious attraction in this case is that Philadelphia gets a state-of-the-art firehouse at almost no cost.

No financial cost, that is. But in outsourcing the project, the city cedes control of an important municipal landmark to a private developer, one that isn’t known for architectural quality. Alterra, you may recall, is the company that gave us Lincoln Square, the striped metal hodgepodge at Broad and Washington. What’s to prevent Alterra from treating the firehouse as just another real estate commodity to be brought in at the lowest possible price? Put another way, what can compel the developer to create a worthy civic landmark?

It may be too late to carve out the firehouse as a pure city project, but it’s not too late for the city to take a firm hand in shaping its design.

Apart from Commissioner Thiel, no one in city government would speak to me about the process for ensuring the firehouse is more than just a glorified garage. But there are disturbing signs. According to a city spokesperson, no one from Public Property or the Department of Planning and Development has yet been assigned responsibility for managing the firehouse project. The last time the city built a new firehouse was 2013, and that building, in Tacony’s Disston Park, is no model. Despite its lush surroundings, it adds nothing to the streetscape.

Alterra’s managing partner, Leo Addimando, told me he plans to hire a firehouse specialist to ensure the Fire Department’s functional needs are met for the new building. That’s good, but not enough. Mayor Jim Kenney should insist that design-savvy staff participate in the negotiations with Alterra and that they continue to oversee the firehouse project until its completion.

One of the downsides of embracing the privatization of public buildings is that the city starts to think like a developer. But public buildings, even modest firehouses, are an expression of our civic aspirations. Because developers often flip their properties after a few years, they want to spend as little as possible up front. But cities build for the long haul. Even though many of our old schools and firehouses in Philadelphia are no longer fit for their original purpose, they remain with us, as housing and offices. These high-quality civic structures remind new generations of what the city was able to accomplish.

Even more is at stake here. Philadelphia has more fires per capita and a higher number of fatalities than any other American city, Thiel says. It also has some of the oldest working firehouses, including one in Chestnut Hill, which opened in 1894. It’s one of the few old firehouses to get an upgrade. Our firefighters deserve better. So do residents, whose lives depend on these buildings.

Firehouses are extremely complex buildings, part garage, part home for their crew of firefighters. But they are also democratic hubs, where we go to cast our votes and seek shelter in emergencies. While they no longer require their distinctive towers to dry fire hoses, they need to be designed in a way that speaks to the aspirations of a resurgent city. Philadelphia has come too far to abandon its ambitions now.