Did he make an assumption about the distance of the sun?
Did he assume parallel rays?

Speaking to all:
How did Eratosthenes get the circumference of the earth?
The length of shadows.
Now for those who believe such a science:

Let us pretend the earth is a ball.
In 24 hours, let us take the distance between the earth and the sun to be constant (not changing) (change negligible).
But in that same 24 hours, no shadow, short shadow, long shadow, very long shadow could be obtained.
So, constant distance, changing shadows.
Inference:
You cannot obtain the distance of the sun from shadows.
Conclusion:
If the distance of the sun cannot be obtained, Eratosthenes is finished!

Let us return to our senses.

'The defence can also be due to unfamiliarity with the subject.'
Plead with YouTube to show you deleted or 'out of algorithm' flat earth videos.

Ball earth makes no empirical sense.
Empirical science is that water cannot stick to a speeding, spinning, wobbling, rotating, revolving fireball from the sun.

Water maintains its level. (Adhesion is between surfaces of different kind).
Water does not bend like a rubber band.
Water does not hang sideways.
Water must be contained.
Water flows.

Flat earth is very empirical.
Globe earth is mostly fascination.
When one studies, he gains knowledge.

Modesty is unpopular too these days.
There is a time to cry and a time to weep.
We hope for a brighter day ahead.
Seems these days are times for rainbows, but by God's grace, all the lights will be brought back to their senses.

Then you can help me change the state of things here.
We must be on fire for truth.
If you love something, you will be happy to discuss it.
Christ and everything about Christ must be spread far and wide.
Luke 8:16
And no man lighting a candle doth cover it with a vessel, or put it under a bed; but setteth it upon a candlestick, that they that enter in, may see the light.

That is why you must think, and decide.
Truth and falsehood are opposed to each other.
The children of light VS the children of darkness.
Judeans vs Gentiles
Watch this and decide https://m.youtube.com/watch?v=8lrBBmZzfvI
Ball earth is total garbage. People are just fascinated about what they can't understand, and become slaves to Google for numbers and figures.
Believe the creation account in the book of Genesis.
Believe God!

OK thanks.

I believe in God and everything written about Him.
Do you believe in Our Lord Jesus Christ?
Confess Him publicly or deny Him.

So why is this the wrong social network?

@SayJess Well, it is deep for some people. But there are others whose parents teach them the truth from youth.
A verible terrible premise is that 'waterfalls fall sideways'.

@SayJess please share with me. What do you find funny?

Sorry. I forgot to end with "The earth is flat classroom students!"