Final answer:
Belief in a spherical Earth can be traced back to Pythagoras, who believed in the perfection of circles and spheres. The ancient Greeks had the knowledge of a spherical Earth, as supported by the observations of Aristotle. The size of the Earth was measured accurately by Eratosthenes using a geometric method.
Step-by-step explanation:
Belief in a spherical Earth can be traced back to the time of Pythagoras, a Greek philosopher and mathematician who lived around 2500 years ago. Pythagoras believed that circles and spheres were perfect forms and therefore proposed that the Earth should be a sphere.
Although Pythagoras is often credited with this idea, it's important to note that the ancient Greeks in general had knowledge of a spherical Earth. Aristotle, another influential Greek philosopher, argued that the Earth was spherical based on observations such as the circular shadow it casts on the Moon during a lunar eclipse and the visibility of certain stars in different regions.
Additionally, the Greeks were able to measure the Earth's size fairly accurately through the work of Eratosthenes, who used a geometric method based on observations of the Sun.