What’s amazing is that the ancient astronomers figured out the precession of the equinoxes caused by a wobble in Earth’s spin axis. A fixed viewpoint would follow a circle in the sky, with the 12 constellations of the Zodiac in that circle. The amazing part is the precession cycle is almost 26,000 years, but they figured it out with very short observation time. No civilization lasted anywhere near long enough to observe very much of the precession arc. I wonder if they had....help?
Unless it were the Nefilim/Anunnaki, who would have reason to use the heavens as a time clock and calendar. Each sign of the Zodiac supposedly corresponded to the length of earth time marking the beginning and end of rulership of the Pantheon members. Also used to determine the location of the rogue planet (Nibiru, original home of the Nefilim) at any given time within its 3,600-year (shar) orbit around the sun. (Re: Sitchin)
I'm sure no man-made clocks/calendars would have lasted that long, except perhaps some of the ancient observatories/temples (including the pyramid) which were oriented (astro-archeologically) to point to zero degrees of the houses.
IIRC, Marduk (son of Enki), according to myth, got his panties all in a wad and started a war to usurp the throne early, claiming that he was allowed to use lunar time instead of solar time.
I've often wondered about this, as well. Even the 19-year Metonic cycle calls for a lot of careful record-keeping by settled people. However, they didn't need thousands of years to observe the effects of precession.
It was understood, or at least recognized, by the 1st century BC, I am told, though the ancients probably did not attribute it to any wobbling in their earth's spin.