Libra is the only sign of the twelve whose figure is an object rather than a living thing, and it is also the latest to be established. In the Greek tradition inherited from Babylon these stars were the claws of the Scorpion, and their Arabic names still say so: Zubenelgenubi and Zubeneschamali, the southern and northern claw. A separate constellation of the balance, MUL ZI-BA-AN-NA, is attested in Mesopotamian sources, and the Roman period fixed the scales as an independent sign, a change some ancient writers connected with the equinox falling there and with the imagery of equal weighing. The scales in Egyptian and Mesopotamian religion are also the instrument of judgment after death, and that association travelled with the figure, giving the sign a weight in the later tradition that a mere seasonal marker would not have carried.
The scales as an independent figure appear to have entered general use only in the late Republic, and some ancient sources connect their adoption specifically to Julius Caesar's calendar reform, since the Roman calendar's realignment brought the autumn equinox closer to this stretch of the ecliptic; the claim is repeated in more than one late antique source but cannot be verified against an earlier, controlling text, so it should be read as a tradition rather than an established fact. The Egyptian tradition, independently of both Babylon and Rome, used a set of balance-scale symbols in funerary art for the weighing of the heart against the feather of Ma'at, a parallel image arrived at without any documented connection to the zodiacal figure.