Thyrea (also Thyraea, Thyreae) was an ancient Greek region, and city in the Peloponnese. It was in modern day Arcadia prefecture, North Kynouria municipality, northwest of Astros.
According to Pausanias 8.3.3, Thyrea was named after a mythological figure: Thyraeos, the son of Lycaon (mythology).
It is the place of the Battle of the Champions between Argos and Sparta. According to Herodotus 1.82[1], Sparta had surrounded and captured the plain of Thyrea. When the Argives marched out to defend it, the two armies agreed to let 300 champions from each city fight, with the winner taking the territory. Presumably the idea was to reduce the total number of casualties. Both armies marched home, so as to prevent either side from helping their champions and escalating the duel into a full battle. They fought until nightfall, when only three men were left: two Argives, Alcenor and Chromius and one Spartan, Othryades. The Argives raced back to Argos to announce their victory, but Othryades remained on the field of battle and stripped the bodies of the Argive dead as prizes, a typical Greek practice. Both sides were able to claim victory: the Argives because more of their champions had survived, the Spartans because their single champion held the field. After quarreling, they fought, and Sparta was victorious. The Spartan survivor, Othryades, was ashamed to be the only man in his unit to live, so he killed himself on the field of battle rather than return to Sparta. Pausanias (10.9.12) adds that the battle was foretold by the Sibyl, and that the Argives considered themselves the victors and dedicated a bronze sculpture of the Trojan horse at Delphi to commemorate the victory. However, Pausanias says that the sculptor of this horse was Antiphanes of Argos, who dates to ca. 400 BC. Therefore, either Pausanias is mistaken, or he is confusing this with a battle at Thyrea in 424 BC.
According to Thucydides (4.56.2) and Pausanias 2.38.5 and 2.29.5, the Spartans gave Thyrea to people from Aigina when they were expelled from their island by the Athenians in 431 BC, during the Peloponnesian War. The Spartans did this for their help against the helot uprising of 464 BC. In 424 BC, during the Peloponnesian War, the Athenians attacked Thyrea, burned the town, and took Aeginetan and Spartan prisoners back to Athens.
In 338 BC, the Argives recovered Thyrea through arbitration (Pausanias 2.38.5).