Tethys was at one time an important goddess in the pantheon of Greek deities, for Tethys was highly regarded as the Greek goddess of the Sea.
Today, Tethys’s fame has been overshadowed by later deities in the Greek pantheon, namely the Olympians, for Tethys was of the preceding generation and was thus one of the Titans.
 Tethys was the daughter of Uranus (Sky) and Gaia (Earth), two primordial Greek deities.
At the time of Tethys’ birth, Uranus was the supreme deity of the cosmos, but due to the intrigue and plotting of Gaia, Uranus was overthrown by the Titans.
Cronus would wield an adamantine sickle to castrate his father, whilst his brothers held their father down; Tethys and her sisters did not play an active role in the overthrow of Uranus.
 All of the Titans though, would benefit from the overthrow of Uranus, for whilst Cronus took up the mantle of supreme deity,
the cosmos was effectively divided between the 12 Titans, with each god or goddess given a sphere of influence.
The role of Tethys in this new order was as a water goddess, although the likes of Pontus and Phorcys had preceded her as Greek water deities.
Tethys though, would primarily be linked with freshwater.
 This role would see her become the wife of the Titan Oceanus, the Greek god of the earth encircling river;
with Tethys and Oceanus believed to be the ultimate source of all the earth’s freshwater.
The “Golden Age” of the Titans would come to an end when Zeus, the son of Tethys’ brother Cronus, rose up against the rule of his father.
This uprising would lead to a ten year war between Zeus, and his allies, against the Titans.
Not all the Titans though stood against Zeus, for all the female Titans, including Tethys, remained neutral, as did some of the male Titans, including Oceanus, the husband of Tethys.
Some stories even tell of Zeus placing his sisters, Hestia, Demeter and Hera into the care of Tethys for the duration of the war.
Zeus would ultimately take the position of supreme
deity after success in the Titanomachy, but having not opposed Zeus,
Tethys and Oceanus were barely
affected by the change in the order of the cosmos.
Nominally, Poseidon, the brother of Zeus, was subsequently in charge of the world’s waters, and he was referred to as the king of the Potamoi,
but Poseidon’ domain did not infringe into that of Oceanus, although Poseidon and Amphitrite would become prominent at the expense of Oceanus and Tethys.
Now it is commonly said that Hera was in the care of Tethys during the Titanomachy, but a less common tale has Tethys nursing the new-born Hera.
In this tale, Hera was not swallowed by her father Cronus, but was secreted away before being imprisoned, just as would happen later with Zeus.
An additional role of Tethys was that of Greek goddess of nursing mothers, by the way.
Tethys is today best remembered as the mother of the 3000 Potamoi and 3000 Oceanids; the Potamoi being the river gods, and the Oceanids the nymphs of freshwater.
Thus, Tethys would supply the 6000 water sources with water drawn from Oceanus.
Certainly there was a strong bond between Tethys and Hera, and when Hera sought retribution against Callisto for having an affair with Zeus, it was to Tethys that Hera went.
In greek mythology, Callisto was a nymph, or the daughter of King Lycaon; the myth varies in such details.
She was one of the followers of Artemis, or Diana for the Romans, who attracted Zeus (Jupiter).
He transformed himself into the figure of Artemis and seduced her in this disguise.
She became pregnant and when this was eventually discovered, she was expelled from Artemis's group, after which a furious Hera(Juno, wife of her seducer) transformed her into a bear.
Later, just as she was about to be killed by her son when he was hunting, she and her son were set among the stars by Zeus as Ursa Major ("the Great Bear") and Ursa Minor.
Hera was not pleased with the placement of Callisto and Arcas in the sky, as the constellations Ursa Major and Ursa Minor, so she asked her nurse, Tethys, to help.
Tethys, a marine goddess, cursed the constellations to forever circle the sky and never drop below the horizon, hence explaining why they are circumpolar.
The goddess Tethys also plays an important role in the story of Aesacus, as it is told in Ovid’s Metamorphoses.
Aesacus was a son of King Priam of Troy who had the ability to see into the future, and thus when Hecuba fell pregnant with a boy
who would become Paris, Aesacus warned his father of the destruction that that new son would bring upon Troy.
Aesacus would fall in love with the nymph daughter of the Potamoi Cebren; the daughter being named Hesperia or Asterope.
The Naiad nymph would step on a poisonous serpent and was killed by the venom.
Aesacus decided that he could not go on living without Hesperia (Asterope) and so decided to commit suicide, and thus the son of King Priam threw himself from the tallest of cliffs into the sea.
Before the fall killed him though, Tethys transformed Aesacus into a diving bird, and so Aesacus did not die, but plunged magnificently into the water.
Far from being pleased at still being alive, Aesacus, now as a bird, tried once again to throw himself from the cliff,
but again the dive of Aesacus broke the surface of the sea cleanly; and yet even today Aesacus, as the diving bird, still plunges from the cliff into the sea.
