The scorpion is a Mesopotamian figure, MUL GIR-TAB, and in Greek myth it is the creature sent to kill the hunter Orion, which is why the two constellations are placed on opposite sides of the sky and never appear together. Its heart is Antares, a red supergiant whose name means the rival of Ares for its colour, another of the four royal stars. The constellation is also the reason for the recurring popular claim of a thirteenth sign: the ecliptic does pass through a corner of Ophiuchus, the serpent-bearer, between Scorpius and Sagittarius, and the International Astronomical Union's constellation boundaries of 1930 make that formally true of the constellations. It has no bearing on the zodiac of the astrologers, which has consisted of twelve equal thirty-degree divisions, not of constellations, since the Babylonian reform of the fifth century BCE.
Manilius treats the scorpion as the most dreaded figure of the whole zodiac, assigning it a violent, martial character consistent with its rulership by Mars, and some Roman sources connect the sign directly to the founding of the Roman legions, another instance, alongside Libra's supposed link to Augustus, of Roman writers reading contemporary institutions into inherited Babylonian figures. The Ophiuchus boundary intrusion noted elsewhere in this entry has a further wrinkle: the IAU's 1930 constellation boundaries were drawn for cataloguing purposes only, without any reference to or intent to reform the tropical zodiac, so treating them as an astronomical correction to astrology, as popular media periodically does, misunderstands what the boundaries were drawn to do.