The myth that Christians in the Middle Ages thought the world was flat was given a massive boost by Andrew Dickson White’s weighty tome The Warfare of Science with Theology published in 1896. This book has become something of a running joke among historians of science and it is dutifully mentioned as a prime example of misinformation in the preface of most modern works on science and religion. The flat Earth is discussed in chapter 2 and one can almost sense White’s confusion that hardly any of the sources support his hypothesis that Christians widely believed in it. He finds himself grudgingly admitting that St Clement, Origen, St Ambrose, St Augustine, St Isodore, St Albertus Magnus and St Thomas Aquinas all accepted the Earth was a globe - in other words none of the great doctors of the church had considered the matter in doubt.
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Some early Christians were victims of misinterpretation. Lactantius rejected the existence of the antipodes - lands on the other side of the equator - on the grounds that anyone who lived there would be upside down. It’s a childish error, but does not mean he also believed the earth to be flat. St John Chrysostom thought the heavens were a box rather than a sphere, but he never says the earth is not a sphere in the centre of the box. Other writers may well have simply been using common language that we still use today. Saying “to the ends of the earth”, “the four corners of the world” or “the sun sank into the sea” does not make you a flat Earther and we should treat ancient people with the same generosity. We can state categorically was that a flat Earth was at no time ever an element of Christian doctrine …