I believe the idea that Columbus thought there was a westward route to India is an urban legend. The idea that the world was round and approximately how large it was, predates Columbus. He just thought there was going to be unknown land out there (and there was). And he had a mix of gospel and pecuniary motives.
“I believe the idea that Columbus thought there was a westward route to India is an urban legend.”
It was his stated purpose when seeking funding for the trip.
Also, to enhance his discovery as fulfilling the terms of his financing, he named the local he found Indios (Indians).
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...
It wasn’t settled science so...