Heraclidae royal-line wife. Wife of Aristodemus, mother of the Spartan twin-kings Eurysthenes and Procles. Per Herodotus 6.52, after Aristodemus died at Naupactus before reaching the Peloponnese, Argeia bore the twins and refused to identify which was the elder when the assembled Spartans pressed her — producing the canonical foundation of the Spartan dual-kingship structure that persisted across the historical period. The Pythia's subsequent oracle (per Hdt. 6.52: that both should be honored as kings, with the firstborn given priority where a distinction was required) institutionalized the Argeia-twin-ambiguity as the Agiad/Eurypontid co-monarchy. The Lacedaemonian and Theban traditions later disputed her ancestry — the Spartan version made her granddaughter of Polynices via Thersander; some traditions made her granddaughter of Autesion son of Tisamenus — both readings tied her to the Theban/Argive royal line and through it to Cadmus, layering the Heraclidae-return narrative onto the older Theban-foundation cycle.