Answer: was known as early as Pythagoras (580-500 B.C.E.)
Explanation: The "realization" that the earth was spherical has been mentioned early in by Greek philosophers.
Even Armenian scientist Anania Shirakatsi (610-685 AD) subscribed to the idea of a spherical Earth.
That was thanks to scientists, philosophers and mathematicians who, as early as around 600 B.C., made observations that Earth was round. Using calculations based on the sun’s rise and fall, shadows and other physical properties of the planet, Greek scholars like Pythagoras and Aristotle determined that the planet is actually a sphere.