[SunkenCiv]

Thanks Robert A Cook PE. The grand banks were being fished well before 1492. Gascons, Basques, people of the Low Countries, and others were expanding the fish catch to compluy with the Papal suggestion of days without meat to cover a supposed meat shortage in Europe, and the Medieval Warming period had caused fisheries to move north. It's well known that the Vikings had settlements in North America, two of them have been located, one was archaeologically excavated over 40 years ago.

Learning had taken off by Columbus' time. It's possible that the idea of a flat Earth has only caught on in quite modern times. Columbus was familiar with the ancient Greek estimate of the circumference of the Earth, but he was also familiar with the existence of a continental mass west of the Atlantic, as he'd been to Iceland to research what he'd already heard about. He also accepted another ancient Greek idea, that all the landmasses were known and were connected (other than islands), so he concluded (incorrectely) that the circumference of the Earth must be much smaller than had been accepted since classical times, and that the lands known to the Gascons, Basques, and Vikings must be the easternmost reaches of Asia.

[Grimmy]

It’s a good thing he got the distance wrong, else he’d have kept on sailing and there was the problem of a whole bunch of land in the way.

[Lonesome in Massachussets]

Astronomy was one of the seven liberal arts in the medieval academic curriculum. Every liberal arts student in medieval Europe was taught that the world was a sphere and learned about the five circles: Equator, the tropics and the Arctic and Antarctic.

https://en.wikipedia.org/wiki/De_sphaera_mundi

Ptolemaic astronomy was based on a spherical earth. No education person in the West, or the Islamic world believed the earth was flat at Columbus’s time.

[Pelham]

“It’s possible that the idea of a flat Earth has only caught on in quite modern times.”

The idea that the ancients thought the Earth was flat is a modern conceit. Romans knew that the Earth is round, as did the Greeks before them.

Any culture capable of sailing over the horizon figured it out.