Massimo

I never understood how they measured time in ancient times. How did they determine the same instant this far away from each other? I mean, I understand sun clocks, but wouldn't that defeat the argument?

With a sundial: simultaneity was guaranteed by the zenith, which could be determined with a sundial. Also, Carl Sagan reports that from documents emerged that Eratosthenes paid a man to walk and measure the distances needed for the calculations.

How did they synchronize the timing of the measurement? Not easy to do from that far apart

I can actually answer that: he measured the only day that the sun was directly above, on summer solstice on Syene. With that he "only" needed to measure the highest angle the Sun would be on Alexandría. No need to sync measurements, or even do one on Syene https://en.m.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth's_circumference …

imagine the effort put into this discovery all those years ago for some oxygen thief in modern times to watch a youtube video and claim it's flat.

Yeah, I was just thinking this too when I watched it. Interesting how a modern flat earther will almost never go through this kind of effort to experimentally confirm their hypotheses...

Hey @FlatEarthOrg