How it was discovered that the earth is round, observations made and conclusions drawn since ancient times, to arrive at the first round the world of a ship.
Because the earth is round
From the way a ship disappeared behind the horizon, men since ancient times thought that the Earth was round.
This was not proven, however, until the first ship went around the world in the 16th century.
Long before, in 240 B.C. about, the Greek astronomer Eratosthenes had calculated exactly the circumference of the Earth.
However no one at what time could believe that Earth was so big.
The Earth, like any other celestial body of considerable size, at least a few thousand kilometers in diameter, is round because this shape constitutes the result deriving from rotation in space.
Each point of its surface is at the same distance from the center and for this reason the spherical shape will be preserved over time.