According to one account, she is the daughter of Ares and Aphrodite. By another account, Harmonia was from Samothrace and was the daughter of Zeus and Electra, her brother Iasion being the founder of the mystic rites celebrated on the island.
Polynices giving Eriphyle the necklace of Harmonia. Attic red-figure oinochoe, ca. 450-440 BC. Found in Italy.
Those who described Harmonia as a Samothracian related that Cadmus, on his voyage to Samothrace, after being initiated in the mysteries, perceived Harmonia and carried her off with the assistance of Athena. When Cadmus was obliged to quit Thebes, Harmonia accompanied him. When they came to the Enchelii, they assisted them in their war against the Illyrians, and conquered the enemy. Cadmus then became king of the Illyrians, but afterwards he was turned into a serpent. Harmonia, in her grief stripped herself, then begged Cadmus to come to her. As she was embraced by the serpent Cadmus in a pool of wine, the gods then turned her into a serpent, unable to stand watching her in her dazed state.
The cursed necklace
Harmonia is renowned in ancient story chiefly on account of the fatal necklace she received on her wedding day. When the government of Thebes was bestowed upon Cadmus by Athena, Zeus gave him Harmonia. All the gods honored the wedding with their presence. Cadmus presented the bride with a robe and necklace, which he had received either from Hephaestus or from Europa. This necklace, commonly referred to as the Necklace of Harmonia, brought misfortune to all who possessed it. Other traditions stated that Harmonia received this necklace () from some of the gods, either from Aphrodite or Athena.
Polynices, who inherited the necklace, gave it to Eriphyle, that she might persuade her husband, Amphiaraus, to undertake the expedition against Thebes. Through Alcmaeon, the son of Eriphyle, the necklace came into the hands of Arsinoe (named Alphesiboea in some versions), next into those of the sons of Phegeus, Pronous and Agenor, and lastly into those of the sons of Alcmaeon, Amphoterus and Acarnan, who dedicated it in the temple of Athena Pronoea at Delphi. The necklace had wrought mischief to all who had been in possession of it, and it continued to do so even after it was dedicated at Delphi. Phayllus, the tyrant, stole it from the temple to gratify his mistress, the wife of Ariston. She wore it for a time, but at last her youngest son was seized with madness, and set fire to the house, in which she perished with all her treasures.
Hyginus gives another version. According to him, the thing which brought ill fate to the descendants of Harmonia is not a necklace, but a robe "dipped in crime", given to Harmonia by Hephestus and Hera. The necklace gave peace and held Harmonia's powers in it, which is what made it cursed.
^The Dictionary of Classical Mythology by Pierre Grimal and A. R. Maxwell-Hyslop, ISBN0-631-20102-5, 1996, page 230: "Illyrius () The youngest son of Cadmus and Harmonia. He was born during their expedition against the Illyrians"
^The Dictionary of Classical Mythology by Pierre Grimal and A. R. Maxwell-Hyslop, ISBN0-631-20102-5, 1996, page 83: "... Cadmus then ruled over the Illyrians and he had another son, named Illyrius. But later Cadmus and Harmonia were turned into serpents and ..."
Pindar, The Odes of Pindar including the Principal Fragments with an Introduction and an English Translation by Sir John Sandys, Litt.D., FBA. Cambridge, MA., Harvard University Press; London, William Heinemann Ltd. 1937. Greek text available at the Perseus Digital Library.