Harmonia ("//; "Ancient Greek: Ἁρμονία), in "ancient Greek religion, is the immortal "goddess of harmony and concord. Her "Roman counterpart is "Concordia, and her Greek opposite is "Eris, whose Roman counterpart is "Discordia. Her siblings are "Eros/"Cupid, "Phlegyas, "Adrestia, and the twins "Phobos and "Deimos. Her parents are the Goddess of Love, "Aphrodite, and the God of War, "Ares.
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. Finally, Harmonia is rationalized as closely allied to "Aphrodite Pandemos, the love that unites all people, the personification of order and civic unity, corresponding to the Roman goddess "Concordia.
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 "Encheleans, 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.
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 (op/uos) from some of the gods, either from Aphrodite or Hera. 
"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 descendents 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.
"Apollonius Rhodius, at "Argonautica, mention about a nymph of the Akmonian Wood, near "Themiscyra, named Harmonia who she was loved by the god Ares and bore him girls who fell in love with fighting, the "Amazons.