In Greek mythology Ortizia (Ancient Greek: Ὠρείθυια) was a queen of the Amazons, daughter of Marpesia and, according to some, of the god Ares.
After the death of her mother in battle, Ortyia became queen of the Amazons and reigned as one half of the diarchy formed with Antiope, possibly her sister. Known for her chastity and for remaining a virgin all her life, unlike the other Amazons, Ortyia was celebrated as an extraordinary warrior who brought much glory to her kingdom.
In his Epitome Marcus Junianus Justin ascribes to Orthyia the role traditionally assigned to Hippolyta in the tale of the twelve labors of Heracles. According to Justin, in fact, Hercules had been urged by Eurystheus to steal Orthyia's belt for him, and the hero set out on the venture with nine ships, with which he occupied the coasts of the Amazon kingdom during the queen's absence.
Taking advantage of the absence of Orthithyia and part of the troops, Heracles easily managed to capture Melanippe and Hippolyta, sisters of Antiope, the queen who remained at home (and thus perhaps of Orthyia herself).
After obtaining the belt, Heracles returned Melanippe to his people, but Theseus claimed Hippolyta as part of his spoils of war and brought her to Athens to make her his wife. Ortizia then gathered an army to give battle to Athens for the purpose of recovering Hippolyta and avenging the defeat inflicted on Antiope.
The Amazons were defeated, but managed to escape and return to their homeland thanks in part to Scythian allies.
Boccaccio recalls her in a chapter of De mulieribus claris.