To me, it’s: That ancient people thought the Earth was flat.
We have records from around 430BC where Greek philosophers spoke of the Earth being a sphere. In 240BC the Greek astronomer Eratosthenes calculated the circumference of the Earth and was only about 2% out.
Yes. It was backed by the oldest book of events at that time.
There were mathematicians that wrote against Galileo, and a notable one, a Dominican I think.
Everything in the past moves to the category of belief.