Edit: Also, it wasn't Egyptians that did this but Phoenicians at the order of the Pharoah.
1- the position of the sun when navigating in the southern hemisphere.
2- claiming a journey of 3 years
It could be a coincidence of course. But then that would make from him a very smart and lucky liar - smart because he had to know the earth was round and lucky, because 3 years, it's what it would likely take to do it.
The second is harder to find an excuse for.
(O/T) Of interest to me is something I learned from HN - https://en.wikipedia.org/wiki/Cape_Bojador - a large rocky shoal off the North Western African coast that scuppered many attempts at sailing around that area. It was, somewhat naively, the first thing in my long life that made me really appreciate how challenging old sea faring would have been.
https://sacredgeometryinternational.com/the-great-pyramid-de...
Beware this type of thing. It’s an introduction to madness.
Some of these pyramid folks claim that they were built as signposts for alien landing strips. And it gets more and more nuts from there.
Herodotus died around 00425 BCE and probably wrote closer to 00435 BCE.
They were all "ancient Greeks" (and Eratosthenes lived in Egypt, so I guess he was an "ancient Egyptian" too) but that doesn't mean they were contemporary. Imagine someone in the year 04542 CE writing, "If the ancient Terrans knew about nuclear energy (as they did, and had unreliable and inefficient fission power plants and nuclear weapons), then Lincoln could have easily used atomic bombs in the US Civil War!" The timespan from Lincoln to Hiroshima was 80 years, from Herodotus to Aristotle about 100 years, and from Herodotus to Eratosthenes about 200 years. And those were very eventful centuries, much like our own.
Knowing the Earth was round, I don't find it hard to imagine that interested minds of the day picked a fruit and toyed with it in hand, squinting a bit and considering the implications.
That is, though the wise could imagine a spherical Earth for as long as they have had fruit, they could just as easily imagine a non-spherical Earth. More easily, I think, because, I mean, look around you, it looks flat. It wasn't until Eratosthenes that the wise lost the ability to believe that the Earth was flat.
There are even more extreme examples of this. The Moscow Papyrus is from 01850 BCE, and it explains how to calculate the area of a hemisphere from its diameter and how to calculate the volume of a truncated pyramid, so this information had already been discovered 3870 years ago—perhaps for many centuries.
Yet what fraction of people today know it? Try asking your taxi driver next time you're on vacation in Perú or the Philippines. Heck, I don't know the pyramid-volume thing myself! I'd have to work it out by integrating a quadratic.
(I recall that studying the calculus as a kid was a bit of a transition for me, because for the first time I came face to face with the realization that most adults' intellectual development was arrested around the year 01583 for some reason. It wasn't that they took a long time to grasp differentiation, or that they had some weird irrational belief at odds with reality, but that they just stopped learning and never grasped differentiation in the decades and decades they lived, converting themselves into intellectual dwarfs. I was still young enough to imagine that somehow I would avoid this...)
I'm not convinced of this finite-space theory. I mean, yes, in a physical sense, there's clearly finite space in your skull. But even the synaptic connections outnumber the bits in the textbooks for a B.A. by about four orders of magnitude, and the potential neural DNA methylation sites outnumber synaptic connections by another six orders of magnitude. So I don't think this intellectual stunting is accounted for by space limitations.
ps: for Russian speaking crowd: there is a YA book https://en.wikipedia.org/wiki/The_Land_of_Foam which is a fiction version of would-be such a trip.