The belief that the Earth is flat was a mode of thought that went out of style during the waning days of the Roman Empire.

But some ideas—like believing the Egyptian pyramids were used to hold grain or that lighting farts is a good use of an open flame—are hard to shake.

That’s what Reddit user doodah360 discovered recently. The redditor posted this kernel in the Today I Learned community: Some people still believe the Earth is a flat disc that it is surrounded by Antarctica with an ice wall guarded by NASA security.

And “some people” doesn’t simply mean that a farmer in Idaho, a cabbie in Glasgow, and a few individuals scattered around the world believe this theory. There is a group that promotes this idea, the Flat Earth Society. It has a website, an online forum (complete with a page debunking a video that claims to debunk flat-earth theory), a wiki, and an online petition asking Google to create a doodle for Jan. 1, 2016, to mark the anniversary of the resurgence of the Flat Earth Movement.

The FES isn’t the only game in town, either. There’s also the International Flat Earth Research Society, a splinter organization that claims the FES “is a controlled opposition group that mixes truth with lies and satire to discredit genuine flat Earth research.”

The beauty of this belief is that it combines the kind of rejection of conventional scientific thought found among climate change deniers and the anti-vaccine movement with a conspiracy theory mentality. It’s not simply that the Earth is a disc, it’s that the US government and all the world powers are actively trying to tell you differently.

Here are the basics behind the beliefs of flat Earthers thanks to the wiki site created by the Flat Earth Society.

What’s a Flat Earth Look Like?

Imagine a coin as the Earth, and then imagine the edge of that coin is actually a giant ice wall—either described as 150 feet or 1,500 feet tall. That’s the world flat Earth believers envision when they think about the plane—and because Earth is a disc, that makes it a plane, not a planet—that they live on. This is how the FES describes it on the group’s FAQ:

“The earth is surrounded on all sides by an ice wall that holds the oceans back. This ice wall is what explorers have named Antarctica. Beyond the ice wall is a topic of great interest to the Flat Earth Society. To our knowledge, no one has been very far past the ice wall and returned to tell of their journey. What we do know is that it encircles the earth and serves to hold in our oceans and helps protect us from whatever lies beyond.”

What Proves the Earth Is Flat?

Although flat Earthers point to a series of experiments to back up their claims, many proponents keep it simple and leave it to their eyes, ears, and other senses to back up their beliefs.

“The evidence for a flat earth is derived from many different facets of science and philosophy,” according to the Flat Earth Society’s FAQ. “The simplest is by relying on ones own senses to discern the true nature of the world around us. The world looks flat, the bottoms of clouds are flat, the movement of the sun; these are all examples of your senses telling you that we do not live on a spherical heliocentric world.”

What About Photographic Evidence of a Round Earth?

Edgar Allan was quoted, “Believe only half of what you see and nothing that you hear.” In the case of photos showing Earth as a sphere, flat Earth believers will tell you to believe nothing you see.

“In general, we at the Flat Earth Society do not lend much credibility to photographic evidence,” an entry in the society’s FAQ states. “It is too easily manipulated and altered.”

Even photos that aren’t intentionally faked to show a round Earth also can fall prey to showing something that isn’t there, according to the society. Photography peculiarities such as barrel distortion—a camera lens effect that gives images the appearance of being spherized—or distortion caused by atmospheric conditions or by the pictures being shot through the bent glass of a pressurized airplane cabin can create misleading visual results.

How Is Everyone Kept Ignorant?

When flat Earthers talk about “The Conspiracy,” they’re not talking about a cover-up to keep people ignorant of Earth’s true shape. They’re referring to the continuing efforts of NASA and other international agencies to deceive the public into thinking the human race has ever made it into outer space.

The Flat Earth Society claims that after a string of failures with its rocket research programs, NASA decided in the late 1960s to adopt a new space exploration strategy: Fake it until they make it. It’s just that NASA still hasn’t made it when it comes to legitimate space travel, so the agency continues the deception. Perpetuating a belief in Earth’s curvature is merely collateral damage caused by the cover-up, according to the FES: