Given the close proximity of South America to Africa, it is a wonder that sailors, especially Portuguese ones, did not sail west in search of the east Indies.....................
It is postulated, but not confirmed by other evidence, that the Basque cod fishermen of North Spain and the east French coast actually were sailing to the cod fish bonanzas off of the NE and Newfoundland coastlines, but kept the location hidden for many, many years.
That said, that two Greeks wrote about a single calculation 1700 years before Columbus, does NOT mean “everybody in Europe knew the diameter of the earth had been correctly calculated”! It means ONE BOOK mentioned TWO Greeks made ONE calculation. Now, over the next 1700 years, how many OTHER PEOPLE wroteclaiming they too knew the earth was round.
Only 50 years earlier, the Portuguese began sailing south around Africa. Very, very slowly south.
“did not sail west in search of the east Indies..”
Earlier ... (perhaps some did but getting back is the problem - just like the vikings/irish monks/fishermen/others are thought/known to have reached the eastern coast of canada centuries before Columbus’ voyages.
It had to do with unfavorable winds in the north atlantic, so sailing far south and then west was the actual route used a great deal and why Brazilians speak Portuguese today. The route up the northern coast america - northeast and then east was the common return route later because of the wind patterns.