Serpens is a northern constellation, one of Ptolemy's forty-eight, representing a great serpent, and it is unique in being split into two separate parts, Serpens Caput, the head, and Serpens Cauda, the tail, divided by the intervening figure of Ophiuchus, the Serpent-Bearer, who is shown grasping the snake. The serpent and its bearer are usually identified with Asclepius, the healer, whose staff entwined with a snake remains a symbol of medicine. Serpens contains the notable Eagle Nebula in its tail. In astronomical tradition the constellation is a star pattern rather than a zodiac sign, though Ophiuchus, which divides it, touches the ecliptic and is the figure invoked in the recurring talk of a thirteenth sign. These are the features of Serpens as the classical and modern traditions describe it, distinct from any astrological reading.
Serpens's western neighbour among the modern constellations is a textbook case of patron flattery in the sky: Scutum, Sobieski's Shield, was introduced by Johannes Hevelius in 1684 to honour his patron, the Polish king John III Sobieski, commemorating his victory at the Siege of Vienna, and it is the sole survivor among a number of similarly flattering seventeenth and eighteenth-century constellations, most of which, honouring various German princes and the King of France's dynasty, did not survive into the standardised modern list of eighty-eight.