The first Flat Earth Society was established in the early 1800s by the English inventor Samuel Birley Rowbotham and remains at the very forefront of 11th Century thinking. ‘Zetetic Astronomy’, as the society prefers to call it, has had to explain away many threats to its principles over the years. 

Things like manned missions to the moon, satellites, photographs of the (round) Earth from space, and endless series of Prof. Brian Cox’s inspirational TV shows. Still, they’ve got 121,000 likes on Facebook, and celebrities who’ve expressed anti-sphere sentiments include B.o.B, Shaquille O’Neal and Freddie Flintoff. Members of the Flat Earth Society claim to believe the Earth is flat. Walking around on the planet's surface, it looks and feels flat, so they deem all evidence to the contrary, such as satellite photos of Earth as a sphere, to be fabrications of a "round Earth conspiracy" orchestrated by NASA and other government agencies. The belief that the Earth is flat has been described as the ultimate conspiracy theory. 

According to the Flat Earth Society's leadership, its ranks have grown by 200 people (mostly Americans and Britons) per year since 2009. Judging by the exhaustive effort flat-earthers have invested in fleshing out the theory on their website, as well as the staunch defenses of their views they offer in media interviews and on Twitter, it would seem that these people genuinely believe the Earth is flat. 

The flat Earth model is an archaic conception of Earth's shape as a plane or disk. Many ancient cultures subscribed to a flat Earth cosmography, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period (early centuries AD), and China until the 17th century. 

The idea of a spherical Earth appeared in Greek philosophy with Pythagoras (6th century BC), although most pre-Socratics (6th–5th century BC) retained the flat Earth model. In the early fourth century BC Plato wrote about a spherical Earth, and by about 330 BC his former student Aristotle provided evidence for the spherical shape of the Earth on empirical grounds. 

Knowledge of the spherical Earth gradually began to spread beyond the Hellenistic world from then on. The flat Earth theory is spreading online, and it’s hard to tell where the joke begins or ends. We can prove that hundreds of thousands of people are aware of an obscure belief that they weren’t before, but we can’t prove whether this has actually converted a substantial number of them to the cause.

108 Questions To The Triangle: Suspicion Makes Us Human