I became convinced of this position about 20 years ago and defended it seriously on the old ASA list. I did graduate work in philosophy 45 yrs ago and so read a whole lot of those early Christian and secular philosophers. All of them believed in a round earth. Most believed the Ptolemaic system, which did have hard to fluid spheres, but they are not the same as the vaulted sky. I think it was Greek influence on the Septuagint translators is what caused them to even translate raqia (a word meaning expansion) as firmament. I think the 70 were trying to look sophisticated.
The ONLY guy I ever found who believed that nonsense was Cosmas Inicopleustes He was a sailor who sailed often to India, proving of course, that the gospel had been taken there. But the dummy should have known full good and well that sails are the first part of the ships to come over the horizon, a sign, of course, of a spherical earth.
Cosmas wrote a very strange book about the flat earth and vaulted sky.I read the thing but hardly found a note worth taking from it.The odd thing is that he was totally ignored by contemporaries and later scholars. No one believed his nonsense, except modern Christians and modern critics of Christianity. lol
This view of Christian topography was pushed by two highly anti-Christian/clergy people,Washington Irving, the novelist and Jeanne Antoine Letrone, a Frenchman. It was too easy an attack on our religion to avoid. All they had to do was ridicule us by saying “Look at what those stupid Christians believed!” and everyone believed them rather than the evidence.
So in my debates years ago I wish I had had access to Wiki because it seems that Wiki at least in one article agrees with my position. I suspect there are people here who will not believe me, so I would point out that the Wiki article notes two modern day celebrities agree with my position. It seems people prefer to believe celebrities than the data:
“According to Stephen Jay Gould, “there never was a period of ‘flat Earth darkness’ among scholars, regardless of how the public at large may have conceptualized our planet both then and now. Greek knowledge of sphericity never faded, and all major medieval scholars accepted the Earth’s roundness as an established fact of cosmology” Historians of science David Lindberg and Ronald Numbers point out that "there was scarcely a Christian scholar of the Middle Ages who did not acknowledge Earth’s sphericity and even know its approximate circumference”."
Frankly, I just think we Christians are gullible to any attack on our religion and believe it implicitly!