Cataclysms are the reason for our wrong chronology
Our actual value (since the Renaissance) of the speed of precession is 72 years for one degree displacement of the spring equinox. This was not always like that.
In the Middle Ages the speed was a bit quicker. As Arab astronomers wrote, the precession speed at their time was around 65 to 66 years per degree, starting from al-Battani (around 880 AD) to Kushayr and as-Sufi until Haraqi (1112 AD). An anonymous contemporary of Zarqallu (11th century) noted likewise 66, and the Latin book of Alfonso X, the Wise (13th century) gives the same value….
… Recently even older dates have been discovered: Dennis Rawlins found an old manuscript in 1981 (published only in 1999) that shows that Aristarchus 130 years before Hipparchus had nearly the same value of 100. (Quoted in German by Sepp Rothwangl, internet). This means once again that an original value for the precession speed had been handed down by the Greeks over something like four centuries. Again I have to admit that we now don’t know when this really was and for how long the speed was uniform. But since the Arabs knew this value it must have been calculated some time before them.
Stepping back again until Babylonian time we suddenly are confronted with the value 50, as Rothwangl asserts quoting cuneiform tablets. The big year of precession, he continues, of the astronomer Kidinnu amounted to 18.000 years thus corresponding to what was passed on by Greeks concerning a phrase of Heraklitus which can only be found in Aetius. Here now the tradition is very weak and contestable, yet lacking other information we can resume the following: From Kepler to us there is the factor 72, while it is 66 for the Arabs and 100 for the Greeks of post-Alexander time; for the Babylonian epoch it was supposedly 50.
http://www.ilya.it/chrono/pages/kataursacheen.htm