[antognini]

Also worth noting that pretty much every ancient civilization ended up figuring out the order of the planets, at least relative to earth. (It turns out not to be so difficult since this is directly related to their sidereal periods.)

[WalterBright]

If you stand at the center of a circle, and have a man walk a circle at radius r from you, and another man walk a circle at radius 2r, it will take the second man twice as long to complete the circle.

It's not a great leap to apply that to the planets.

But it's not proof that the planets were ordered that way.

Science happens when one invents an explanation for observed phenomena, and then the explanation (theory) makes a prediction, then an experiment is devised, and the theory is validated if the prediction matches the theory, or tossed aside if it doesn't. In other words, the scientific method. That appeared fairly recently, and the consequences were an explosion of knowledge.