The Science of Discworld IV

medieval times the Earth was thought to be a flat disc, but the evidence is ambiguous, except very early on. Around AD 350 St John Chrysostom deduced from the Bible that the Earth floated on the waters below the firmament of heaven, a view shared by St Athanasius at much the same time. In about AD 400 Bishop Severian of Gabala considered the Earth to be flat. Unusually, he also believed that the Sun did not travel beneath it during the hours of darkness, but instead nipped back round to the north, hidden from view. By 550 Cosmas Indicopleustes, an Egyptian monk, was doggedly following Egyptian tradition and offered theological arguments for a flat Earth, but with a new twist: the shape was that of a parallelogram surrounded by four oceans.
    Many medieval writers definitely knew the world was round, although many believed that no humans lived on its underside, the antipodes. The important regions of the world formed a hemisphere, and in drawings and text it was easy to confuse this with a flat disc.A famous case is the seventh century AD Bishop Isidore of Seville, who wrote in his
Etymologiae
: ‘The mass of solid land is called round after the roundness of a circle, because it is like a wheel. Because of this, the Ocean flowing round it is contained in a circular limit, and it is divided into three parts, one part being called Asia, the second Europe, and the third Africa.’
    At first sight, ‘round’ here seems to mean a flat disc, not a sphere. Maps of the period, known as T and O, T-O, O-T, or
orbis terrarum
maps, draw a round O outside a capital T. This divides the O into three parts: Asia above the horizontal stroke, Europe and Africa to the left and right of the vertical stroke. Rotate it through a right angle and it looks much like a modern map, though distorted. The oceans all join up and there is a complete ring of water surrounding the land. However, the map could be a projection into the plane of a hemisphere, and that seems to be the prevailing opinion among scholars today. On the other hand, the statement that the oceans are ‘contained in a circular limit’ is difficult to reconcile with a round Earth, especially since the reason is stated to be ‘it is like a wheel’. Do the scholars protest too much?
    Be that as it may, there are many references from early Christian times indicating knowledge of a round Earth, but that raised a more difficult theological issue. A round Earth requires the existence of antipodal regions, diametrically opposite to the geographical regions that were then known to Europeans. The existence of these regions wasn’t a problem, but there was general disbelief that they were, or could be, inhabited. The objection was not that people would fall off, but that no one had been there to see whether there was any land – and if there were, whether there were
people
. It was a perfectly scientific objection: the problem was lack of evidence. Shortly after the sack of Rome in 410, Saint Augustine of Hippo addressed the issue in his
City of God
:
    … as to the fable that there are Antipodes, that is to say, men on the opposite side of the Earth … that is on no groundcredible … Although it be supposed or scientifically demonstrated that the world is of a round and spherical form, yet it does not follow that the other side of the Earth is bare of water; nor even, though it be bare, does it immediately follow that it is peopled … Since these people would have to be descended from Adam, they would have had to travel to the other side of the Earth at some point … It is too absurd to say, that some men might have taken ship and traversed the whole wide ocean, and crossed from this side of the world to the other, and that thus even the inhabitants of that distant region are descended from that one first man.
    Full marks for geography, then.
    The history of flat versus round Earth is complex, open to many divergent interpretations, and littered with myths. A common one is that Columbus had to overcome a widespread belief that the Earth was flat in order to persuade the Spanish royal family to allow him to try to sail westwards to India. Actually, the main obstacles were twofold: the correct belief that the round Earth was too big for this to work according to Columbus’s schedule, and the cost.
    Columbus fudged the figures.
    Educated people seriously began to wonder whether the Earth really might be flat, or at least not the conventional spheroid, in the Victorian era,