Castor and Pollux/Dioskouroi. Castor and Pollux were twin half-brothers in Greek and Roman mythology, known together as the Dioscuri. Their mother was Leda, but they had different fathers; Castor was the mortal son of Tyndareus, the king of Sparta, while Pollux was the divine son of Zeus, who seduced Leda in the guise of a swan. Though accounts of their birth are varied, they are sometimes said to have been born from an egg, along with their twin sisters Helen of Troy and Clytemnestra. In Latin the twins are also known as the Gemini or Castores, as well as the Tyndaridae or Tyndarids. Pollux asked Zeus to let him share his own immortality with his twin to keep them together, and they were transformed into the constellation Gemini. The pair were regarded as the patrons of sailors, to whom they appeared as St. Elmo's fire. They were also associated with horsemanship, in keeping with their origin as the Indo-European horse twins. There is much contradictory information regarding the parentage of the Dioscuri. In the Homeric Odyssey, they are the sons of Tyndareus alone, but they were sons of Zeus in the Hesiodic Catalogue. The conventional account combined these paternities so that only Pollux was fathered by Zeus, while Leda and her husband Tyndareus conceived Castor. This explains why they were granted an alternate immortality. The figure of Tyndareus may have entered their tradition to explain their archaic name Tindaridai in Spartan inscriptions, or Tyndaridai in literature, in turn occasioning incompatible accounts of their parentage. Their other sisters were Timandra, Phoebe, and Philonoe. Castor and Pollux are sometimes both mortal, sometimes both divine. One consistent point is that if only one of them is immortal, it is Pollux. In Homer's Iliad, Helen looks down from the walls of Troy and wonders why she does not see her brothers among the Achaeans. The narrator remarks that they are both already dead and buried back in their homeland of Lacedaemon, thus suggesting that at least in some early traditions, both were mortal. Their death and shared immortality offered by Zeus was material of the lost Cypria in the Epic cycle. The Dioscuri were regarded as helpers of humankind and held to be patrons of travellers and of sailors in particular, who invoked them to seek favourable winds. Their role as horsemen and boxers also led to them being regarded as the patrons of athletes and athletic contests. They characteristically intervened at the moment of crisis, aiding those who honoured or trusted them. Ancient Greek authors tell a number of versions of the story of Castor and Pollux. Homer portrays them initially as ordinary mortals, treating them as dead in the Iliad, but in the Odyssey they are treated as alive even though the corn-bearing earth holds them. The author describes them as having honour equal to gods, living on alternate days because of the intervention of Zeus. In both the Odyssey and in Hesiod, they are described as the sons of Tyndareus and Leda. In Pindar, Pollux is the son of Zeus while Castor is the son of the mortal Tyndareus. The theme of ambiguous parentage is not unique to Castor and Pollux; similar characterisations appear in the stories of Hercules and Theseus. The Dioscuri are also invoked in Alcaeus' Fragment 34a, though whether this poem antedates the Homeric Hymn to the twins is unknown. They appear together in two plays by Euripides, Helen and Elektra. Cicero tells the story of how Simonides of Ceos was rebuked by Scopas, his patron, for devoting too much space to praising Castor and Pollux in an ode celebrating Scopas' victory in a chariot race. Shortly afterwards, Simonides was told that two young men wished to speak to him; after he had left the banqueting room, the roof fell in and crushed Scopas and his guests. Both Dioscuri were excellent horsemen and hunters who participated in the hunting of the Calydonian Boar and later joined the crew of Jason's ship, the Argo. During the expedition of the Argonauts, Pollux took part in a boxing contest and defeated King Amycus of the Bebryces, a savage mythical people in Bithynia. After returning from the voyage, the Dioscuri helped Jason and Peleus to destroy the city of Iolcus in revenge for the treachery of its king Pelias. When their sister Helen was abducted by Theseus, the half-brothers invaded his kingdom of Attica to rescue her. In revenge they abducted Theseus's mother Aethra and took her to Sparta while setting his rival, Menestheus, on the throne of Athens.