"Circle" does not denote "sphere." It more properly denotes "tabletop." Early Hebrew cosmology (from the book of Enoch) saw the Earth as flat, with the sky as a solid dome overhead. The stars were equivalent to angels and they, and the sun and moon, entered the dome through doors in its base, traversed the sky along set routes, and exited through doors on the other side.
Of course, the book of Enoch is not a part of the Scripture. The Hebrew word used in Isaiah 40 is chug - which can also mean circuit or sphere. This is one of the few places in Scripture that it is used. Although many may have believed the earth was flat - the Bible didn't say so. It was Christians who first posited the theory that the earth was a round sphere and then put their lives on the line by hopping in little boats and going out on the ocean to prove it. In fact, as you are probably aware, until the government schools of Europe and America became virulently anti-Christian in the 20th century, many advances in science in the prior 300 years was made by devout Christians.