What do these five Philadelphia locations have in common:

Each site was left in limbo for years, sometimes decades, thanks to City Council’s use of a clubby parliamentary practice known as councilmanic prerogative. Although the name sounds genteel and mannerly, the maneuver can turn an ordinary, mild-mannered district councilperson into power-mad feudal lord. No matter what craziness a local representative proposes, the rest of Council will vote in lockstep, no questions asked, knowing the favor will be returned when they want approval for a special measure in their own district. Usually the special bills involve property sales and zoning.

Councilmanic prerogative — sometimes called legislative courtesy — has been around in some form in Philadelphia for at least a century, according to a 2015 report by the Pew Charitable Trusts, but it has increasingly made the news. That’s in no small measure a result of Philadelphia’s development boom, which has turned once-unwanted city property into a hot commodity. But the more that district Council members interfere, the harder it is for the city to make the best use of its vacant property.

Just last month, Councilwoman Jannie Blackwell nearly derailed the sale of the city’s long-vacant Provident Mutual Insurance building at 4601 Market after she invoked the prerogative. Turns out, according to a report by Plan Philly’s Jake Blumgart, she was seeking to extract concessions for a favored campaign donor, Michael Karp, a West Philadelphia landlord who is so wealthy, he just paid $20 million for a Manhattan townhouse. Not only does councilmanic prerogative turn every district representative into a meddling mini-mayor, it removes transparency from city property sales.

The prerogative is being used to smooth the way for favored developers to acquire city land at discount prices. As my colleagues William Bender and Mark Fazlollah have documented, a childhood friend of Kenyatta Johnson was able to buy several city-owned parcels on the cheap and then double his money by flipping them. A bargain land deal also happened in Darrell Clarke’s district.

This corrosive practice thrives in Philadelphia because of two unfortunate provisions in the city’s Home Rule Charter. When that otherwise progressive document was adopted in 1951, it limited the powers of the Planning Commission while giving the final word on land sales and zoning changes to City Council. The result is that a single district councilperson often decides which city-owned properties can be sold and who can buy them. The Planning Commission and Redevelopment Authority are obliged to carry out the directives.

Not that any of this is spelled out in the charter. The practice resembles the unwritten “Gentleman’s Agreement” that once prevented developers from building anything taller than City Hall tower or, perhaps, the mob’s legendary code of omerta. The prerogative exists because it’s mutually beneficial for the 10 geographically based district representatives, who form the majority of the 17-seat Council. Anyone who dares vote against a fellow member’s bill will surely be shunned. It’s political suicide.

Blackwell’s attempt to hold up the Provident sale failed after her behind-the-scenes machinations became public. The incident prompted a rare backlash from residents, who rallied in support of the city’s plan to turn the building into a public health campus. Those constituents were so angry that they crashed her campaign kickoff and demanded an end to the prerogative.

For sheer chutzpah, few uses of the prerogative can compare with what happened in 1986 after the city reached a deal to lease Penn’s Landing to Willard Rouse, the developer who famously broke the Gentleman’s Agreement to build Liberty Place. Rouse needed Council’s approval to complete the transaction, and the local councilman, Leland Beloff, promised to make that happen — for $1 million.

Unfortunately for Beloff, Rouse reported the shakedown to the FBI and was wearing a wire when he dropped off the cash. Beloff was sentenced to 10 years in jail. But the city’s suffering has gone on much longer. Three decades later, Penn’s Landing remains a parking wasteland.

Today, Council members are more likely to take their thank-yous in a legally acceptable form: campaign contributions. When Thaddeus Bartkowski sought permission in 2015 to build a trio of freestanding digital billboards in Center City, he showered donations on the two local councilmen who controlled the districts where they would be placed: Mark Squilla and Kenyatta Johnson.

While objections from PennDot ultimately kept those billboards from going up, the prerogative frequently ends up prolonging blight. Four years after Cindy Bass scuttled the sale of the historic Germantown YWCA to developer Ken Weinstein, that fragile building still sits empty. Society Hill remains home to a suburban-style supermarket on Fifth Street because Squilla created a special zoning provision to sabotage construction of a five-story apartment building on the site. The prerogative “costs the city money,” says Weinstein, an outspoken opponent of the practice.

It also ruins neighborhoods. West Philadelphia’s Spruce Hill section, home to one of America’s best collections of Victorian architecture, is being dissembled house-by-house for cheap student residences because Blackwell has blocked the creation of a historic district — not once, but twice.

The practice even compromises the safety of Philadelphia residents. The city has been unable to implement many of its Vision Zero street safety initiatives because Council members have objected to bike lanes and other improvements. They use councilmanic prerogative and “then nothing happens,” complains the Bicycle Coalition’s Randy LoBasso.

Council members will often defend the prerogative by arguing that the local representative knows his or her district best. But, as practiced in Philadelphia, the courtesy goes against a fundamental democratic concept: checks and balances. As you may recall from middle-school civics class, the legislature exists to check the power of the executive and prevent a single person from becoming a tyrant. But when a district councilperson can introduce a bill, approve a land sale, or change zoning — all without real oversight from fellow legislators — there is no check on that power.

We tend to think of councilmanic prerogative as an aberration that distorts Philadelphia’s Council process. In fact, it underlies the whole system. Council’s control over individual land sales is a big reason that the new Land Bank is nearly moribund. It’s why Mayor John Street’s Neighborhood Transformation initiative accomplished so little.

Is there any hope that the system could change in Philadelphia, as it has in other cities? In 2011, I wrote a column suggesting that the introduction of the new zoning code might make the practice obsolete by reducing the need for zoning changes. Wrong.

Some opponents of the prerogative, like the Center City District’s Paul Levy and Philadelphia 3.0’s Jon Geeting, suggest that new blood on Council could lead to reform. I’m doubtful. The power of the prerogative is just too tempting.

It’s true that the prerogative does occasionally produce a positive result. This week, Clarke used his position to introduce a bill to rezone St. Laurentius Church in Fishtown and put an end to a nuisance lawsuit that has delayed its renovation for apartments. Of course, given the popularity of the cause, the bill (which will be voted on next week) would probably have passed even without the prerogative.

Perhaps the solution is to create a better balance between Council and the city’s planning professionals. Justin DiBerardinis, who is running for an at-large Council seat, has been advocating for a charter convention to look at prerogative and other issues. No argument there. If Philadelphia ever hopes to realize its potential as a modern city, it’s going to need a constitution fit for the 21st century anyway. One where councilmanic prerogative doesn’t have the final word on the look of the city.