'Achaea of Phthia') or simply Phthiotis (Φθιῶτις) was a historical region of Thessaly, in ancient Greece.
[1] Inhabited by perioikoi, it was originally formally not a part of Thessaly proper but a Thessalian dependency, and had a seat of its own in the Delphic Amphictyony.
[1] Phthiotis was inhabited by the Phthiotic Achaeans (Ἀχαιοὶ Φθιῶται), under which name they are usually mentioned as members of the Delphic Amphictyony.
This district, according to Strabo, included the southern part of Thessaly, extending from the Maliac Gulf on the east, to Dolopia and Mount Pindus on the west, and stretching as far north as Pharsalus and the Thessalian plain.
The cities of Phthiotis were: Amphanaeum or Amphanae, on the promontory Pyrrha and on the Pagasaean Gulf; Phthiotic Thebes, Eretria, Phylace, Iton, Halus, Pteleum, Antron, Larissa Cremaste, Proerna, Pras, Narthacium, Thaumaci, Melitaea, Coroneia, Xyniae, Lamia, Phalara, and Echinus.