If I recall correctly, archeologists had (a few years back) come to the conclusion that the Babylonians had originally had THIRTEEN zodiacal signs.
In addition to the twelve well-known zodiacal signs, they had also recognized the constellation of Ophiuchus (the Snake-Bearer) as a zodiacal sign.
Of course, this would require shortening the remaining 12 periods.
I noted it especially because my astrological sign would then have shifted from Sagittarius to Ophiuchus.
Regards,
[snip] As is the case with all of the Zodiac constellations, Ophiuchus was recorded in the 2nd century by the Greek astronomer Ptolemy, and the name is Latin for “serpent bearer.”
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The Babylonians associated the constellation with Nirah, a god who was sometimes depicted with a human upper body and legs that were serpents.
Ophiuchus is the 13th sign of the Zodiac in astrology (which is not a science) and represents those born between Nov. 30 and Dec. 17. [/snip]
https://www.space.com/21759-ophiuchus.html
[snip] There is no evidence of the constellation preceding the classical era, and in Babylonian astronomy, a “Sitting Gods” constellation seems to have been located in the general area of Ophiuchus. However, Gavin White proposes that Ophiuchus may in fact be remotely descended from this Babylonian constellation, representing Nirah, a serpent-god who was sometimes depicted with his upper half human but with serpents for legs.[57]
The earliest mention of the constellation is in Aratus, informed by the lost catalogue of Eudoxus of Cnidus (4th century BCE)... Ophiuchus is one of the thirteen constellations that cross the ecliptic.[65] It has sometimes been suggested as the “13th sign of the zodiac”. However, this confuses zodiac or astrological signs with constellations.[66] The signs of the zodiac are a twelve-fold division of the ecliptic, so that each sign spans 30° of celestial longitude, approximately the distance the Sun travels in a month, and (in the Western tradition) are aligned with the seasons so that the March equinox always falls on the boundary between Pisces and Aries.[67][68] Constellations, on the other hand, are unequal in size and are based on the positions of the stars. The constellations of the zodiac have only a loose association with the signs of the zodiac, and do not in general coincide with them. [/snip]
https://en.wikipedia.org/wiki/Ophiuchus