Libra symbol (♎)

Where the twelve sign glyphs came from is not known. Encyclopaedia Britannica says their history is unknown and that they first appear in Greek manuscripts of the late Middle Ages. Allen cites Clerke, who found them in manuscripts of about the 10th century but in carvings only from the 15th or 16th, and Brown, who quotes the antiquary C. W. King: King found the glyphs on no antique work and suspected “Arab sages” had devised them, a view Brown did not share. The balance beam and Brown’s altar are both readings of the shape; neither is documented.

The early Greeks did not see a balance in these stars. Allen says many have thought the Scales replaced, in comparatively recent times, the Chelae, the Claws of the Scorpion, which had been a separate part of a double sign. Eratosthenes counted the Claws’ stars in the Scorpion; Hipparchos also called them Ζυγόν or Ζυγός, the yoke or beam; and Geminos, with Varro, first used the Yoke as a star name, calling it the sign of the autumn equinox. The familiar story that the Scales were invented for the equinox, when day and night weigh the same, Allen calls a statement “often seen”, current as early as the Roman poet Manilius.