Aethra
Aegeus, ruler of Athens, was unable to have children with his wife, so he went to seek the advice of an oracle. The oracle warned him not to open his wine flask until he reached the highest point in Athens. Aegeus didn't understand the oracle's advice. Disappointed, he went to visit the king of Troezen. The king got Aegeus drunk and sent his daughter, Aethra, to his bed chamber. She and Aegeus made love, but that same night she left his bed to make a sacrifice. Poseidon approached her, and this pair also made love. (Some myths say she was raped by Poseidon and that the whole situation was set up by Athena.)
Aethra conceived a child that night — but no one knew whether the father was Aegeus or Poseidon. Most believed that the child was Poseidon's, although Aegeus claimed the child, a son, as his own. The child, Theseus, became a famous hero.
Amymone
Amymone was one of the fifty daughters of King Danaus. The king sent Amymone and her sisters to find water in the land of Argos. Poseidon had caused the region to dry up, so locating water seemed an impossible task. After walking for many miles, Amymone became tired and decided to rest. Left alone, she was approached by a satyr. (Another myth states that Amymone, in pursuit of a deer, accidentally hit the satyr with a spear.) The satyr attempted to rape the girl, but Poseidon interceded, using his trident to chase away her attacker.
Poseidon proceeded to court Amymone for himself. After making love to her, Poseidon used his trident to create a spring so Amymone could bring water back to her family. (Some myths tell the story a bit differently, saying that Poseidon did not create the spring intentionally but accidentally struck a rock with his trident while chasing the satyr.) Amymone succeeded in her goal of finding water, and Poseidon succeeded in adding another lover to his list.
Amymone and Poseidon had a son from their union: Nauplius, whose extensive knowledge of the seas and astronomy would make him a hero to seafarers. Nauplius also founded the town of Nauplia, a famous naval port near Argos.
Demeter
Another of Poseidon's conquests was his sister Demeter. Wishing to escape her brother's advances, Demeter transformed herself into a mare. But Poseidon wasn't to be put off. He transformed himself into a stallion and mated with her in a pasture, both of them in the form of horses.
Together they produced Desponia, a nymph, and Arion, a wild horse. Desponia was worshiped alongside her mother in Arcadia. The people there erected statues of the mother and daughter as women with mares' heads. Arion was a famous winged horse who could speak. Some myths say that his right feet were like a human's.
Iphimedia
Iphimedia was an unhappily married woman. Her husband, Aloeus, a son of Poseidon, was also her uncle. Iphimedia was in love with Poseidon and made a habit of walking along the seashore. She would often sit down and scoop up the water, allowing it to flow over her breasts. Poseidon found this alluring, and his union with Iphimedia produced two sons: the Giants Ephialtes and Otus.
Medusa
Medusa was a Gorgon, with snakes for hair and a terrifying appearance that could turn anyone to stone. Some myths say, however, that Medusa wasn't always this fearsome creature. In these myths, she was once a beautiful woman, and her beauty caught Poseidon's eye.
Poseidon approached Medusa as she was visiting one of Athena's temples. They made love in the temple — an act unacceptable to the virgin goddess Athena. As punishment, Athena turned Medusa into the horrifying creature she is known as today. However, this transformation wasn't enough for Athena; she also helped Perseus to slay Medusa.
When Perseus cut off Medusa's head, two children appeared — Chrysaor and Pegasus — the results of her union with Poseidon. Some myths say that Chrysaor was born from Medusa's neck and Pegasus from her blood. Others say that both were born when drops of Medusa's blood landed in the sea.
Chrysaor means “the man with the golden sword”; he was born wielding a golden sword. He would grow to marry Callirrhoe (an Oceanid) and father two children: Geryon (a Giant with three heads) and Echidna.
The second son, Pegasus, was a winged horse, who would later play a role in several myths. Pegasus was wild and free until tamed by either Athena or the hero Bellerophon (depending on which myth you read). At the end of his days, Pegasus was changed into a constellation.
Theophane
Theophane was a beautiful young woman who had several suitors, including Poseidon. To avoid competition, the sea god abducted Theophane and took her to an island.
Theophane's suitors searched for their missing love. They eventually discovered where she was, but before they could reach her Poseidon turned the island's inhabitants to sheep — including Theophane. At the same time, Poseidon transformed himself into a ram. When the suitors arrived on the island and found nothing but a big flock of sheep, they decided to have a feast. As they prepared to slaughter the animals, Poseidon changed the sheep into wolves that slaughtered the suitors instead.
Poseidon and Theophane mated while in their sheep forms, so their son (whose name is not recorded) was born a ram. But this wasn't just any ram — he had a fleece of gold and was able to speak and fly.
Thoosa
Thoosa was the daughter of Phorcys (a son of Gaia). Her affair with Poseidon is known mostly for its offspring: the Cyclops Polyphemus. Polyphemus was not one of the original race of Cyclopes. Instead, he was a violent, savage, man-eating creature.
