Augustine, On the City of God 16.9
In an influential passage, Augustine is not convinced by the idea that people live on the other side of the globe.
quod vero et Antipodas esse fabulantur, id est homines a contraria parte terrae, ubi sol oritur quando occidit nobis, adversa pedibus nostris calcare vestigia: nulla ratione credendum est. neque hoc ulla historica cognitione didicisse se adfirmant, sed quasi ratiocinando coniectant, eo quod intra convexa caeli terra suspensa sit, eundemque locum mundus habeat et infimum et medium; et ex hoc opinantur alteram terrae partem, quae infra est, habitatione hominum carere non posse.
As for the story they tell that there are also Antipodes – that is, men on the opposite part of the earth, where the sun rises when it sets for us, who walk with their feet opposite to ours – in no way is this to be believed. People affirm that they have not learned this through any historical knowledge, but they conjecture by reasoning, on the grounds that the earth is suspended within the convexity of the sky, and that the world has the same space beneath as above; and from this they suppose that the other part of the earth, which is below, cannot be without human habitation.