About 2,000 years ago, when science was nowhere near as advanced as it is today, when people hadn’t crossed the seemingly endless oceans separating the continents and observation of Earth from an external vantage point was impossible, most civilizations around the world believed the planet to be a flat surface, often depicted as a plane covered by a circular dome of the sky.

This conception, which held Earth to be a flat surface, is called the flat Earth theory. And while it was already being disputed, based on empirical evidence, as long ago as the 6th century BCE, in some places such as ancient Greece, it persisted in different parts of the world till much more recently, such as in China, where the belief was prevalent till the 17th century.

While it is a misconception that the belief was widespread in Europe during the Middle Ages (the Earth had already been circumnavigated by 1521), there still exist societies to this day that promote the illogical belief, which is contrary to all evidence, including actual photographs of the planet taken from space.

The most prominent of the modern groups that believe the Earth to be flat is the Flat Earth Society, which claims on its website: “This is the home of the world-famous Flat Earth Society, a place for free thinkers and the intellectual exchange of ideas. This website hosts information and serves as an archive for Flat Earth Theory. It also offers an opportunity to discuss this with the Flat Earth community on our forums.”

Earlier this year, the rapper known as B.o.B. seemed to endorse the theory as well when he went on a Twitter rant.

Anthony Scaramucci, a Wall Street investor and an adviser to President-elect Donald Trump, in an interview Wednesday likened the science behind climate change to the flat Earth theory, saying scientists didn’t always get things right.