The constellation of Libra is not connected to any myth and it is the only one of the Zodiac, to "represents" an object rather than a living creature. Originally the area it occupies belonged to the Scorpion, representing its claws. In ancient times many were those who would have chosen not to change the shape of the Scorpion, and limit the Zodiac to eleven constellations.
Virgil, instead, preferred the creation of a new constellation, corresponding to the birth ofOctavian Augustus, and in the Georgics intentionally writes that the Scorpion rolls itself up to give way to Libra.
As to why this shape was chosen, it has been suggested that the scales representing the concept of equality, they are to be related to the fact that over two thousand years ago, due to the precession of the equinoxes, that area contained the fall equinoctial point, and therefore day and night had equal length.
It is also likely that the Greeks dedicated the constellation to the goddess of justice, holding blindfolded a balance in hand, to symbolize impartiality.
Amongst the Romans, instead, the scales were held by Caesar, with reference to his wisdom and justice.
The constellation is not clearly visible, both because it is not high on our horizon, and because it has no conspicuous stars. It occupies an area of 538 square degrees and is entirely southwards. Its main stars, Alpha and Beta, are in the middle of the alignment between Spica, in Virgo, and Antares, in Scorpius. Libra culminates in the South between 10 p.m. and 11 p.m. at the end of June, and the Sun crosses it from 29 October to 21 November.