The idea that everything was made up of 4 elements (or a rather a combination of those) also assumed a round earth. Early things are heaviest and sink to the bottom, water is lighter than earth, air lighter than water and fire is lighter than air (that’s why the stars, made up of fire, are at the very top)
The church never disputed the earth being round. They were pretty adamant about it being the center of the cosmos though, with the sun orbiting it.