Orthus

In Greek mythology, Orthrus was, according to the mythographer Apollodorus, a two-headed dog with a serpent-tail who guarded the crimson cattle of the giant Geryon, who lived on the far-west island of Erytheia alongside the Hesperides. Orthus, along with his master Geryon and the herdsman Eurytion, was killed by Heracles as part of his tenth labour, when he was sent to steal the cattle for king Eurystheus. According to Apollodorus, Herakles killed Orthrus with a single strike from his olive club, although in art Orthrus is sometimes depicted pierced by arrows poisoned with Hydra venom. Orthus maintains a consistent celestial theme, seen in the etymological background of his name, association with the "sunset" island of Erytheia, and ascendancy myth.

Orthus was the first of the many monsters spawned by the she-dragon Ekhidna. His many siblings included the three-headed hound of Hades, Kerberos, the Lernean Hydra, and the three-headed hybrid Khimaira. With the latter he fathered the Sphinx and the Nemean Lion, although in other traditions they are his siblings, also born from Ekhidna.

Depictions of Orthrus in art are rare, and he is always shown in connection with the theft of Geryon's cattle by Herakles. He is usually shown dead or dying, and sometimes pierced by one or more arrows. The earliest depiction of Orthrus is found on a late seventh-century bronze horse pectoral from Samos. While according to Apollodorus, Orthrus had two heads in art, the number shown varies. While Orthrus is usually depicted with two heads, from the mid sixth century onward he is sometimes depicted with only one head, and one early fifth century BC Cypriot stone relief gives him three heads, á la Kerberos. He is also usually depicted with a snake-tail, but sometimes with only a dog-tail.

Orthus bears a close resemblance to his brother Kerberos, and his sometimes called his "doublet". Like Orthus, Kerberos was multi-headed, and because Erytheia was sometimes considered to be located in the afterlife, Geryon was also considered a guard dog of Hades. The earliest accounts gave Kerberos fifty, or even one hundred heads, though in literature three heads for Kerberos became the standard. However, in art, often only two heads for Kerberos are shown, like Orthus. Cerberus was also usually depicted with a snake tail, just as Orthus usually was. Both became guard dogs and both were overcome by Herakles in one of his labours. This makes distinguishing the two brothers in art difficult and contextual clues become vital to correct identification.

Orthus' name was derived from the original Greek name Orthros, from the word orthros meaning "twilight," or Orthos, from orthos, meaning "virtuous, morally upright". His name was latinized as Orthrus and Orthus, respectively.

Some say that Orthus' original owner was Atlas, the titan who carried Heaven on his shoulders, and only came to be owned by Geryon after Atlas was shackled. It is said that after being killed by Herakles, Orthus ascended to heavens and became the star Sirius (The Dog Star), which is the brightest star in the night sky.

The poet Pindar refers to the "hounds of Geryon" trembling before Heracles. Pindar's use of the plural "hounds" in connection with Geryon is unique. He may have used the plural because Orthus had multiple heads, or perhaps because he knew a tradition in which Geryon had more than one dog.