>>which the Egyptians had calculated circa 200BCE, to the remarkable accuracy of ~1%

Minor nit: Eratosthenes was a Greek who lived in Alexandria - a Greek city founded by Alexander of Macedon on the shore of then-conquered Egypt. Alexandria was very much part of the Hellenistic world. Also, there's some dispute over how close he got, mostly having to with which 'stadia' (Greek measure of distance) as several were in use when he was alive. But, yes, you can come within 1% using his technique - so you're not wrong.

Just bringing this up because 'Egyptians' implies much longer ago than the Hellenistic era.