In 2014, the owners of a block of luxury apartments in central London drew widespread outrage after installing rows of small metal spikes on the ground outside the building to deter homeless sleepers. A photo of the spikes was met with immediate indignation on Twitter, and the mayor of London himself condemned them as “ugly, self-defeating, and stupid.” It’s not hard to see why the architectural feature—which has long since been removed—caused such an outcry. Metal spikes are both noticeable and unambiguous in their purpose, an explicit visual reminder to outsiders that they are not welcome. However, there are plenty of more subtle but equally unwelcoming types of urban design being utilized by cities all over the world, intended to control and alienate segments of their population.

The controversial anti-homeless spikes were a classic example of hostile architecture, sometimes more euphemistically referred to as defensive architecture or unpleasant design. Hostile architecture is meant to discourage people from using public spaces in unconventional ways and is hardly a new phenomenon. A historical example can be found on the roads between New York City and Long Island, which have famously low overpasses. This was an intentional choice by the famous (now infamous) planner Robert Moses, who built the bridges too low for public buses to pass under. In doing so, he prevented anyone who could not afford to drive a car—primarily low-income families of color—from traveling to Long Island’s theoretically public parks and beaches.

Moses’ use of civil engineering to enable discrimination is a classic instance of hostile architecture, but more modern examples abound. Small metal skateboard deterrents are often placed along railings or ledges to stop skaters from using them as ramps. Public restrooms sometimes have blue lighting to prevent drug users from shooting up inside (by making it harder to see their veins). Speakers emitting a high-pitched noise audible only to people under a certain age have been placed on both public and private property to discourage teenagers from loitering.

Although skaters, drug users, and adolescents are all frequent victims of hostile architecture, it should come as no surprise that the most common targets are the homeless. Architects and city planners have come up with numerous ways to stop people from sleeping in public spaces, ranging from the obvious to the nearly invisible. The controversial spikes outside the London apartment building were not the first nor the last instance of spikes being used to keep people off a flat surface. Some buildings, including the Strand Bookstore in New York and (ironically enough) Saint Mary’s Cathedral in San Francisco, periodically douse the pavement outside with sprinklers, soaking anyone who happens to be resting there. And public benches are often tilted, unconventionally shaped, or divided into individual seats to prevent anyone from lying down on them.

Although the spikes outside the London apartments were a notable exception, most instances of hostile architecture simply go unnoticed. If you never need to sleep on a park bench, it is easy to ignore that park benches are getting harder and harder to sleep on. Most of us are privileged enough to move blithely through our environment without considering how it might be manipulating us. Whether we notice it or not, it’s happening regardless. Urban design is a powerful political tool because of its perceived neutrality, and nowhere is this clearer than in its continued use in the fight against the homeless.

Note that I have referred to urban design as part of a fight against the homeless, not homelessness. This is no mistake. Poverty and homelessness are real and complex problems, but hostile architecture is the worst possible solution because it addresses the symptoms and not the underlying causes. Stopping a homeless person from sleeping in a public park will not help them find food, a job, or a home. It will only make them invisible to the rest of us. Rather than addressing homelessness in any meaningful way, hostile architecture allows public officials to conceal the issue and pretend it no longer exists. This is an unethical and unsustainable approach, and if we don’t start to look critically at the design of our public spaces, we risk complicity. A greater consciousness towards what lies behind urban planning, not just what appears on the surface, is an important tool in understanding how cities interact with their homeless (or their people of color, their drug addicts, or their youth). How do our surroundings affect what we see and how we are subtly controlled? Think about the influence that physical structures have on people and their more direct and damaging effect on marginalized populations. The cruelty of hostile architecture may be hard to spot, but it’s time we started looking harder.

Tara Joy can be reached at tjoy@wesleyan.edu.