Earth is (always has been) round, so why have the flat-out wrong become so lively?

Until the 17th century, the Fens—a broad, flat swath of marshland in eastern England—were home only to game-hunters and fishermen. Eventually, though, their value as potential agricultural land became too enticing to ignore, and the Earl of Bedford, along with a number of “gentlemen adventurers,” signed contracts with Charles I to drain the area, beginning in the 1630s. A series of drainage channels were cut, criss-crossing the wetlands of Cambridgeshire and Norfolk. The plan was a qualified success; a vast area was now farmable, though wind-powered pumps were needed to keep the water at bay.

The most notable feature of the Fens is their pancake-like topography. It’s said that if you climb the tower of Ely Cathedral on a clear day, you can make out the silhouette of Peterborough Cathedral, some 30 miles to the northwest. Indeed, one could see even further if it wasn’t for the curvature of the Earth.

Enter one Samuel Birley Rowbotham, a 19th-century inventor and quack doctor who went by the name “Parallax.” Rowbotham believed that the Earth was flat, and that the Fens were the perfect place to prove it. In particular, he set his sights on the Old Bedford River, one of the 17th-century drainage cuts built under the tenure of the Earl of Bedford. The river—it’s really a canal—runs straight as an arrow for some 22 miles, from Earith, Cambridgeshire, to Downham Market, Norfolk, where it meets the River Great Ouse.