The Greek scholar Eratosthenes accurately calculated the circumference and by corollary that the Earth was round in the third century BC...
Columbus studied the writings of Eratosthenes, and one reason he was looking for a way West is because the Muzzies had cut off access to the Silk Road, and had made it very risky for Christian Europeans to avoid robbery, pillage and murder at their hands going West to East by land...
The Crusades came 400 years prior and apparently didn’t take care of that problem... yet, somehow what became of that issue? Trade seems to have been okay once the American colonies got under way.