The Ancient Greeks

Championed by Aristotle, the the theory of a Round Earth began in antiquity, contradicting the prevailing belief of a Flat Earth. Aristotle founded his theory on three proofs, which are still in use today as evidence for the rotundity of the Earth. As Greek and Roman influence and culture spread throughout the ages the concept of a Round Earth established itself as the cornerstone of Western civilization.

Aristotle's Round Earth Proofs

There are three proofs Aristotle gave for the supposed rotundity of the earth. They are:

• Ships Appear to Sink as They Recede past the Horizon
• The Shadow on the Moon During a Lunar Eclipse Is Round
• The Southern Constellations of the Night Sky Appear to Rise as You Travel Southwards

Eratosthenes' Shadow Experiment

Eratosthenes is famed for his shadow experiment where he determined the circumference of the Round Earth and the distance to the sun. However, this experiment assumes that the earth is a globe and that the sun is far away. The experiment can also be interpreted under a Flat Earth model as well. See:

• Eratosthenes on Diameter
  
• Distance to the Sun

Continuous Universe

The Ancient Greeks believed in a Continuous Universe. This Ancient Greek concept of a perfect universe assumes the following:

• That perfect circles can exist
• That one could zoom into a circle forever and see a curve
• That any length of space can be divided into infinitely smaller parts
• That the space can be infinitely long
• Time can likewise be infinitely divided, or infinitely long
• Light rays travel in perfectly straight lines into infinity
• The Perspective Lines receded infinitely and continuously into the distance

Quotes

  “ Although we condemn flat-Earth thinking as an example of foolish ignorance, a spherical Earth is actually counterintuitive. It’s such a radical idea that it has been ‘discovered’ only once, in Athens after 400 BCE. The concept of the Earth being round didn’t appear in any other civilisation. India and the Islamic world learnt it from the Greeks, while China had to wait until the Jesuits arrived in the 16th century and turned the Chinese view of the Universe upside down. ”
                  —Historian of science Dr.James Hannam (bio), author of "God’s Philosophers: How the Medieval World Laid the Foundations of Modern Science" (Source)