In Western world since 4000 yrs ago, the earliest models of the earth were statistical (predicting sun, moon, weather for crops) - they just didn't think about the shape of the earth. The Greeks are the first well known people to develop a geometric model of the earth. It was straightforward to do measurements to determine the rough geometry and size of the earth.

The sky was more difficult due to the distance, and they split into two speculative camps: Pythagoras (earth orbits sun orbits central furnace) and Aristotle (earth as center of the universe). The telescope (an invention financed and published by Pope Urban viii, patron of Galileo) allowed measurements capable of distinguishing these models. (With a result much to the consternation of establishment science.)