I thought we weren't able to chart their orbits and thus know their orderings until the last few centuries. I'm sure we recognized them as being brighter than stars, visible as more than points of light, with non-sidereal motion, and we gave them names. But I don't think we knew Saturn was 6th "prehistorically".
"... an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the known universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day. He was influenced by the concept presented by Philolaus of Croton (c. 470 – 385 BC) of a fire at the center of the universe, but Aristarchus identified the "central fire" with the Sun and he put the other planets in their correct order of distance around the Sun.[2]"
