Ever wonder why your city chooses to adorn its sidewalks and public parks with such ugly benches? It turns out that these structures aren't just offensive to the eyes.

Unsightly public architecture isn't always simply a product of bad taste — it can also serve as a means of social control and aims to repel local homeless populations, Atlas Obscura reported.

What makes architecture "hostile"?

Known as hostile, defensive, or disciplinary architecture, these structures are strategically designed to deter homeless people and other groups perceived as undesirable from sleeping or loitering within eyesight of local residents.

"This style of architecture, which makes use of spikes, barricades, protrusions and checkpoints to prevent society’s unwanted from inhabiting public spaces, is not new," reporter Allegra Kirkland wrote on Alternet in 2015. "But its forms are proliferating, and it can now be found in urban centers across the globe, from Tokyo to Copenhagen."

This is what it looks like.

In 2014, a luxury apartment building in London installed “anti-homeless” spikes in a nearby alcove.

"People living in the flats, which sell for upwards of £800,000, said the metal studs were installed two weeks ago after a number of homeless people were seen sleeping there," the Telegraph reported in June 2014.

The spikes led to major backlash on social media, and they were ultimately removed.

Hostile architecture isn't always easy to spot.

Hostile architecture also pops up in more subtle forms — like public benches.

Often, defensive architecture is said to be installed for security purposes, but our definitions of safe and secure housing are colored by the stigma and criminalization of homelessness. "This style of design cannot be untethered from broader anti-vagrancy efforts, particularly in the United States," Alternet reported.

"We see these measures all the time within our urban environments, whether in London or Tokyo, but we fail to process their true intent," writer Alex Andreou wrote on the Guardian. "I hardly noticed them before I became homeless in 2009."

"It was only then that I started scanning my surroundings with the distinct purpose of finding shelter and the city’s barbed cruelty became clear," he continued.

Andreou described what happened when he discovered an old wooden bench had been replaced with a more hostile design:

"An old, wooden bench, made concave and smooth by thousands of buttocks, underneath a sycamore with foliage so thick that only the most persistent rain could penetrate it. Sheltered and warm, perched as it was against a wall behind which a generator of some sort radiated heat, this was prime property. Then, one morning, it was gone. In its place stood a convex metal perch, with three solid armrests. I felt such loss that day."

Not all hostile architecture is ugly, either. It can even come in the form of a pretty plant, placed somewhere homeless people might otherwise sleep or rest.

"Hostile design comes in even more innocuous, and sometimes even lovely forms," Atlas Obscura pointed out. "Take the humble potted plant. What could be hostile about a leafy ficus in a pretty pot? Nothing—until you consider where it's placed."

Hostile architecture attempts to conceal poverty and homelessness, which are already criminalized in many U.S. cities.

There are already many laws that criminalize homelessness in the U.S., as Alternet activism editor Alyssa Figueroa pointed out in a February 2015 piece. These laws restrict homeless individuals from activities like resting, begging, sharing food, and urinating in public.

"Hostile architecture facilitates the work of law enforcement by making it physically impossible for the homeless to inhabit public spaces," Kirkland observed on Alternet. "Neither approach actually addresses the root causes of homelessness, but instead shoves it out of sight."

[h/t Atlas Obscura]