Picture of Ophiuchus, between Scorpius and Saggitarius.
...the twelve zodiac signs-Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius and Pisces- were amongst the first constellations to be devised. With the exception of Libra, the scales, which was a later addition, the zodiac signs are all living creatures. The term 'zodiac' derives from the Greek word for 'animal'.
The faint constellation of Libra, the scales, lies between the constellations of Virgo and Scorpius. The Sun passes through this constellation during November. However, this part of the sky was not always designated Libra: it was at one time part of the adjacent constellation of Scorpius, occupying the area of the scorpion's claws. The Greeks referred to this area as Chelae, the claws and Ptolemy described the constellation both as Chelae and as Libra. It is difficult to establish who first introduced the constellation of Libra. One conjecture is that it originated with the Sumerians, who, around 2000 BC, referred to the constellation as 'the balance of heaven'.