They already knew it was round by watching ships rise up from the horizon. Also, the fact that you can't see Egypt from Crete. If the earth was flat, the sea an

They already knew it was round by watching ships rise up from the horizon. Also, the fact that you can't see Egypt from Crete. If the earth was flat, the sea and earth wouldn't 'pull away' as it went into the distance, it would shrink to a vanishing point and you'd notice the difference.