A mythic water snake inhabiting the marshes of Lerna, south of Argos in Greece. The Hydra had multiple heads, from 9 to 100 in various sources, though Pausanias (2.37.4) was sure that there had really been only one; if severed, these heads could regenerate in multiple form. Slaying the Hydra was Heracles' second canonical labor, which he accomplished after much difficulty with the aid of Iolaus; the trophy of his victory was a set of arrows poisoned with the creature's blood. That poison eventually dyed the shirt of Nessus and occasioned Heracles' own death. Both the Hydra and the Crab (Cancer), which Hera sent to help it in the fight, became constellations.
The battle with the Hydra, usually as part of a series on Heracles' labors but sometimes treated on its own, became a standard subject for artists from the late 15th century onward. Antonio del Pollaiuolo painted it for the Palazzo Medici (ca. 1460); now lost, it is known through other sources. John Singer Sargent included it in his murals for the Boston Museum of Fine Arts (1921-1925). An ancient statue of Heracles unearthed at Rome ca. 1620 was restored by Alessandro Algardi, perhaps correctly, as a depiction of the hero with the defeated monster. From 1738 until 1817 the Hydra gave its name to the Stanza d'Ercole in the Capitoline Museum and was one of the prime exhibits until moved elsewhere. There are modern sculptures as early as Alfonso Lombardi (ca. 1525), as recent as Mathias Gasteiger (1930); reliefs adorn a bronze roundel from the 1490s by the Mantuan artist known as Antico, and a popular line of silver vases designed by John Flaxman (1805-1806).
In literature there are no important narrations of the story as such; its main life is as a vehicle for metaphor. Medieval and Renaissance mythographers, citing the etymological connection with hydōr ("water"), often treat the myth as an allegory of the difficulties of swamp reclamation. In The Hydra Head (La cabeza de la Hidra, 1978), Carlos Fuentes's novel about late 20th-century Mexico, the treacherous fluid is petroleum. Plato, in a much noted passage (Euthydemus 297C), likens Heracles' labor against the Hydra to that of arguing with Sophists; the motif later became a commonplace figure for single-minded truth struggling with endlessly resourceful error. In The Faerie Queene (1590-1596) Edmund Spenser uses the Hydra for similes about the creature attendant on the giant Orgoglio, a brutal champion of the Roman Catholic Church (1.7.17), and about the Blatant Beast, the noisy slanderer of courtly virtue (6.12.32, the head count here rising to 1,000). On the other side of the Channel, the slaughter of Protestants on and following Saint Bartholomew's Day 1572 was celebrated with a medal likening the event to the killing of the Hydra. Horace, to different effect, had cheerfully used the Hydra as an image of Rome's imperial success in the 1st century bce (Odes 4.4.61-68), and Christopher Marlowe's Tamburlaine (ca. 1587) makes the same celebratory identification:
as the heads of Hydra, so my power, Subdued, shall stand as mighty as before. If they should yield their necks unto the sword, Thy soldiers' arms could not endure to strike So many blows as I have heads for thee. (1 Tamburlaine 3.3.140-144)
Paul Valéry imagines the adversaries mingled in blessed repose and release after their struggle:
Beneath the footsteps of the stars Sleep, victor, slowly decomposed, For the Hydra latent in the hero Unfolds out to infinity. ("Ode secrète," in Charmes, 1922)
In 1756 Carolus Linnaeus appropriated the name Hydra for a class of freshwater organisms, related to jellyfish, with impressive regenerative powers; the largest is an inch long.