How did the Greeks and Romans figure out that the earth is round not flat?

Aristotle provided the first conclusive argument for a spherical earth when he noted during a lunar eclipse that the shadow the earth cast on the moon was circular.

Lactantius of Alexandria was an early apostate from the scientifically based cosmology of the ancients. In “On the False Wisdom of the Philosophers,” a chapter in his copious Divine Institutions (A. D. 302-323), he ridicules the idea of a spherical earth in the most simplistic and nearsighted terms.

The devout author scoffs at the image of people with their feet above their heads, rain falling upward, mountains hanging on without support; and he flatly denounces the possibility of heavens lower than the earth.

The Fathers of the Church championed increasingly narrow and literal interpretations of the Scriptures, deriving the shape of the earth and motion of the planets from Genesis and fragmentary passages throughout the sacred text. The Huns who overran Europe and toppled the Roman Empire lent a helping hand to this effort to extinguish classical learning.

Severianus, Bishop of Gabala, a leader of the Syrian Church in 360, held the heavens to be a tabernacle, a theory popular among many patristic writers, on the basis of Isaiah 40:22: “It is he that stretcheth out the heavens as a curtain and spreadeth them out as a tent to dwell in Severianus taught that the sun does not pass under the earth at night but travels through northern parts, as if concealed behind a wall. “The sun also ariseth, and the sun goeth down, and hasteth to his place where he arose” (Ecclesiastes 1:5). In winter, he argued, the days are shorter because the sun takes longer to travel its nightly course.

Although the Fathers of the Church never established an organized and detailed cosmology, a well-traveled merchant named Kosmas Indicopleustes wrote 12 books on the subject between 535 and 547.

As part of his elaborate theory of the universe as tabernacle, in which the earth appears as a rectangular table of shewbread (loaves that were offered to the Lord every Sabbath), he points out that this plane is higher in the north and west, for ships traveling in this direction are sluggish compared with those sailing south and east. Similarly, the Tigris and Euphrates flow along more readily than the Nile. Kosmas maintains that at night the sun goes behind a mountain, near the top in summer, resulting in a short night; along the base in winter, bringing long hours of darkness.

Hrabanus Maurus, Abbot of Fulda and later Archbishop of Mainz, decided in the 9th century that the earth was round, like a wheel, but he had to reconcile this with the Scriptures that speak about the four corners of the world. The solution for him was to put the square inside a circular horizon, and give heaven two doors through which the sun could pass.

By this time, however, the Greek and Roman writings had again gained credence and were moving westward, overturning the tables of the tabernacle, making way for the gods of science.