Picture this: You’re out for a walk in your local park, and you start to feel a bit tired.

Fortunately, you see that there’s a bench nearby. You sit down, catch your breath, and enjoy the fresh air. You’re so comfortable that you almost drift off—and, in the process, you almost fall off of the bench. The sloped surface won’t hold you for long. In fact, it’s slightly uncomfortable. You start to get a bit angry: why would the city pay for such a shoddily designed bench?

As it turns out, the city planners know exactly what they were doing. The structure in question might look something like this.

Located in Japan, this particular installation is touted as an “anti-homeless” bench. It’s designed to be inconspicuous, but it has a devious purpose: Give tourists a place to catch their breath while sending the homeless on their way.

In fact, many city planners choose designs that discourage loitering. You might have seen benches in your own town with “armrests” that prevent tired citizens from laying down. Others have shallow, tilted seats, which allow a person to get comfortable—but not too comfortable.

The goal is to force the homeless to leave an area by denying them a basic human comfort. In recent years, this type of “defensive architecture” has spread, prompting numerous discussions regarding the role of architecture in modern society.

The issue can be contentious. In 2014, owners of an apartment complex in London sparked an international outrage when they installed metal studs near the building’s entrance. The studs, conspicuously placed in a single area and not visible from the street, sent a clear message to the homeless people in the area.

Anti homeless floor studs. So much for community spirit 🙁 pic.twitter.com/Yz8VF7Ryid — Ethical Pioneer (@ethicalpioneer) June 6, 2014

“There was a homeless man asleep there about six weeks ago,” a resident of the area told The Telegraph at the time. “Then, about two weeks ago, all of a sudden, studs were put up outside. I presume it is to deter homeless people from sleeping there.”

The spikes were reportedly removed several weeks after the story went viral.

Opponents of defensive architecture have another name for it: hostile architecture.

Regardless of its name, it’s nothing new. According to some experts, hostile architecture has existed for hundreds of years. It certainly existed in the early United States; just look at the Miles Brewton House in Charleston, South Carolina. In 1822, the house’s owners added a spike-laden bar above its entrance to defend against the possibility of a slave revolt.

Modern public structures often use novel, artistic aesthetics to hide their functionality. For instance, a bench in Camden, London, uses a sloped surface to prevent citizens from laying down. Unless you know what you’re looking for, you probably wouldn’t recognize the problem with the design. If you’re homeless, however, you certainly won’t feel welcome.

Other designs use attractive cobbled stone to give tourists some eye candy—while preventing panhandlers from sitting or laying on certain surfaces. Rounded windows might have subtle studs to prevent anyone from sitting against them. Underpasses might have metal rails that route water through them, drenching any homeless people who might duck underneath to get relief from the rain.

To homeless rights advocates, these types of designs have nefarious implications.

“People are being criminalized for sitting or sleeping in public spaces,” Jonathan, a spokesperson for the Western Regional Advocacy Project (WRAP) tells Urbo. WRAP is an organization dedicated to protecting the civil and human rights of the homeless.

“If you don’t want people using a public space, don’t call it a public space. That kind of defeats the purpose of it … It’s very expensive to be poor, especially with the vagrancy laws all over,” he says. “You get a ticket for sitting too long, for sleeping in a car. The only option we give homeless people is to keep walking.”

Advocates for the homeless say that defensive architecture sends a not-so-subtle message to the underprivileged: You’re not welcome here.

With that said, urban architecture is also frequently used to discourage other “undesirable” behaviors.

Many property services offer decorative skate deterrents, which prevent skaters from grinding their boards on handrails and other smooth surfaces. Some designs look fairly ornate, so they’re not immediately noticeable to non-skaters. They are, however, obstacles designed to curb certain behaviors.

Skaters are one thing—but wildlife? Believe it or not, some municipalities are employing similar tactics to prevent birds from making messes on the luxury vehicles below their perches. The video below details the controversial “anti-bird spikes” that line the trees in an affluent England neighborhood. Sounds bad, looks worse:

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Property owners in the United Kingdom seem particularly fond of defensive design (or, at least, their newspaper writers seem fond of covering the phenomenon). In Nottinghamshire, England, residents approved a measure to install pink spotlights over an area where local teenagers had been gathering.

The bright pink lights reportedly “highlighted skin blemishes,” driving the youth away from the area.

“The pink lights are indiscriminate in that they will impact on all young people and older people who do not, perhaps, have perfect skin,” Peta Halls, development officer for the National Youth Agency, told the BBC in 2009. “…[Teens] have a right to congregate. It’s part of being a teenager, and most young people are good, law-abiding people.”

Some people have fought against defensive architecture with mixed results. German sculptor Fabian Brunsing satirized the movement with “Pay & Sit: The Private Bench,” a bench with rounded spikes that only retract when a “patron” inserts a few coins. Alas, the idea was a bit too clever; The Metro reports that officials at Yantai Park in Shangdong, China copied the art installation’s design, but without the sarcastic context.

“This seems like a fair way to stop people grabbing a bench at dawn and staying there all day,” an official reportedly said.

Of course, the most obvious defensive architecture designs often cause controversy.

Well-executed projects don’t tend to attract much attention. After all, the purpose of defensive architecture is to control behavior without explicitly changing the rules of public areas. Many of the projects are all but invisible to the average pedestrian, and while uncomfortable armrests or studded sidewalks may be an occasional inconvenience, they’re not a serious problem for most people.

That’s part of the reason why these projects can seem offensive: They’re set up to hide their true purpose. They affect impoverished people more than they affect others, and to some human rights advocates, that’s unacceptable.

While defensive architecture isn’t particularly objectionable when it’s designed to scare off birds or send skateboarders to the skate park, advocates for the homeless say that it goes too far when it explicitly targets the poor. After all, why should a city protect the rights of one social class over another? Why show a lack of compassion towards a certain group of people?

“It’s crazy that [cities] go all that way to be a jerk, rather than say, ‘Let’s address this severe poverty,'” the WRAP spokesperson says. “Why spend time and millions of dollars to hide the problem when you can potentially solve it?”

Unfortunately, solving the problem isn’t so easy.

Homelessness isn’t a new issue for cities in the United States, and according to WRAP, defensive architecture isn’t doing much to help the situation. The 1977 federal budget drastically cut housing assistance programs, and homelessness became a serious health policy issue in the 1980s. WRAP contends that the federal government made homelessness into a local issue, and many cities simply refused to deal with the problem.

“Every year, we keep making cuts to public housing programs and expecting extreme poverty and homelessness to go away,” Jonathan says.”Since we haven’t put back the funding into public housing, people find themselves homeless, living in the street. The cities’ reaction is to make that a crime.”

“In California, on average, we have about eight laws in each city to criminalize extreme poverty. Instead of talking about housing, we created laws to criminalize the presence of people.”

California approved a $2-billion bond to help house the homeless. Two years later, not a penny has been spent. https://t.co/ENXEFdqWOb pic.twitter.com/XnStokdWPf — Los Angeles Times (@latimes) March 4, 2018

The hostile architecture, Jonathan says, is a symptom of a much bigger problem: Cities want the homeless to go away, but they can’t devote resources towards preventing homelessness. Until society makes a collective effort to address homelessness, social justice advocates say that more cities will look towards defensive architecture for a quick fix.

“People need to educate, organize, and protect human rights,” Jonathan says. “When you see somebody trying to throw human rights to the floor, you need to stand up and speak up. They say they don’t want homeless people in my town, tell them, ‘Get out of here—the city’s for everyone, not just the people you want.'”