Thetis

A prophecy ends two divine courtships

Thetis was a Nereid, one of the sea goddesses born to Nereus and Doris. The early Greek poet Hesiod lists her among their 50 daughters. She is one sister in a large sea family, yet a prediction about her child decides what the gods on Olympus do.

The gods Zeus and Poseidon both want Thetis, until the goddess Themis speaks. She says Thetis will bear a son stronger than his father, with power greater than the thunderbolt of Zeus or the trident of Poseidon. Neither god is willing to become the next father overthrown by his own child.

Their answer protects their rule by changing Thetis’s future. She will marry a mortal, Peleus, so any stronger son will be mortal too. The poet Pindar presents the match as an honour given to a man who respected the gods. For Thetis, the prophecy has made her both a prize and a danger, and it gives her no choice about the marriage planned around it.

How Peleus holds her

The Centaur Chiron tells Peleus to seize Thetis and keep his grip through every change of shape. In his arms she becomes fire, water and a wild animal. He lets her go only after she returns to her own form.

Her changes are resistance. They are not a test she chose to set for a bridegroom. Peleus wins because a male adviser tells him how to hold out against her power until it can no longer free her. The gods then celebrate the wedding on Mount Pelion and bring gifts, including an ash spear from Chiron and the immortal horses Balius and Xanthus from Poseidon.

Ancient writers disagree about why the marriage is forced on her. Pindar treats it as a sensible answer to the prophecy of Themis. Apollodorus, whose book the Library retells the Greek myths, also keeps another version. In it, Thetis refuses Zeus out of loyalty to the goddess Hera, who raised her, and Zeus angrily marries her to a mortal. The poet Apollonius puts the same claim in Hera’s own speech. One account rewards Peleus; the other punishes Thetis.

The hiding place on Skyros

Their child is Achilles. Apollodorus tells of an early attempt by Thetis to protect him. She knows Achilles will die if he sails with the Greek expedition to Troy. So she dresses him as a girl and hides him among the daughters of Lycomedes on the island of Skyros.

The hero Odysseus comes with gifts suited to the women and hides weapons among them. A trumpet sounds. Achilles reaches for the weapons and gives himself away. The disguise fails because the qualities that make him useful to the expedition also make hiding him impossible.

On Skyros, one blast of a trumpet is enough to send Achilles back onto the path his mother has spent his life trying to close.

What a goddess can do for her son

In the Iliad, Homer’s epic poem of the war, Thetis already knows her son’s life will be short. Agamemnon, the leader of the Greek army, takes Briseis from Achilles and shames him. Achilles calls to the sea. His mother rises from the water, listens and promises to plead with Zeus.

She clasps the knees of Zeus and asks him to let the Trojans win until the Greeks see what Achilles is worth. Zeus agrees, though he expects Hera to be angry. Thetis can steer the war through a power her son does not have. But the Trojan success she wins helps bring about the fighting in which Achilles’s friend Patroclus dies.

After that death, Achilles decides to go back to battle, though he knows what will follow. His armour was taken with Patroclus’s body, so Thetis goes to Hephaestus, the smith god. He remembers that she sheltered him after his fall from Olympus, and he makes a new shield, helmet, breastplate and leg guards.

The armour meets the need of the moment. It cannot save Achilles from death. Thetis herself says he is fated to die soon, and every gift from the gods equips him to move closer to that end. She can change her own shape, reach Zeus, enter the house of Hephaestus and hide her son under another identity. None of those powers changes the prophecy that rules them both.