Aristotle around 350 BC "observed" the world to be a sphere from lunar eclipses - that and other things it was generally accepted among the educated way back then. Now a bit later on in 240 BC we had Eratosthenes do his shadow compares on the summer solstice from two different cities a known distance apart. Easy to look up the exact simple calculations for this and do it yourself even... he was pretty close to the actual circumference we know it to be now. Despite the uneducated flat earthers... NCSWIC!!!
Aristotle around 350 BC "observed" the world to be a sphere from lunar eclipses - that and other things it was generally accepted among the educated way back then. Now a bit later on in 240 BC we had Eratosthenes do his shadow compares on the summer solstice from two different cities a known distance apart. Easy to look up the exact simple calculations for this and do it yourself even... he was pretty close to the actual circumference we know it to be now. Despite the uneducated flat earthers... NCSWIC!!!