In Greek mythology Phthia (; Greek: ? or ? Phthía, Phthí?) was a city or district in ancient Thessaly. It is frequently mentioned in Homer's Iliad as the home of the Myrmidones, the contingent led by Achilles in the Trojan War. It was founded by Aiakos, grandfather of Achilles, it was the home of his father Peleus, his sea-nymph mother Thetis, and his son Neoptolemus, who reigned as king after the Trojan War.
Phthia is referenced in Plato's Crito, where Socrates, in jail and awaiting his execution, relates a dream he has had (43d-44b): "I thought that a beautiful and comely woman dressed in white approached me. She called me and said: 'Socrates, may you arrive at fertile Phthia on the third day.'" The reference is to Homer's Iliad (ix.363), when Achilles, upset at having his war-prize, Briseis, taken by Agamemnon, rejects Agamemnon's conciliatory presents and threatens to set sail in the morning; he says that with good weather he might arrive on the third day "in fertile Phthia"--his home.
Phthia is the setting of Euripides' play Andromache, a play set after the Trojan War, when Achilles' son Neoptolemus (in some translations named Pyrrhus) has taken the widow of the Trojan hero Hector as a slave.
Mackie (2002) notes the linguistic association of Phthia with the Greek word phthisis, meaning "consumption, decline; wasting away" (In English, the word has been used as a synonym for tuberculosis) and the connection of the place name with a withering death, suggesting a wordplay in Homer, associating Achilles' home with such a withering death.
The Homeric Catalogue of Ships speaks of Achilles' kingdom as follows (Iliad book 2.723-8):
Now again all those who dwelt in Pelasgic Argos:
those who dwelt in Alos and Alope and Trachis
and those who held Phthia and Hellas with its fair women,
and who were called Myrmidons and Hellenes and Achaians;
of those fifty ships the leader was Achilles.
These names are generally believed to have referred to places in the Spercheios valley in what is now Phthiotis in central Greece. The river Spercheios was associated with Achilles, and at Iliad 23.144 Achilles states that his father Peleus had vowed that Achilles would dedicate a lock of his hair to the river when he returned home safely.
However, a number of ancient sources, such as Euripides' Andromache, also located Phthia further north in the area of Pharsalia. Strabo also notes that near the cities of Palaepharsalus and Pharsalus there was a shrine dedicated to Achilles' mother Thetis, the Thetideion. Mycenean remains have been found in Pharsalus, and also in other sites nearby, but according to Denys Page, whether the Homeric Phthia is to be identified with Pharsalia "remains as doubtful as ever".
It has been suggested that "Pelasgic Argos" is a general name for the whole of northern Greece, and that line 2.723 of the Iliad is meant to serve as a general introduction to the remaining nine contingents of the Catalogue.