The Ancient Greeks believed that one in 300 Greeks was a traitor. Ancient society was merciless to traitors and considered them a burden of the earth, subhuman, scum and likened them to a dirty disease that polluted the air of the city.
Here are three of the most well known traitors of Ancient Greece:
The "subhuman" who equated his name with treason not only in Greece, but all over the world, was Malieus Ephialtes, son of Eurydis, one of the greatest traitors in history as he showed Persian King Xerxes the narrow path from the Kallidromos that led Thermopylae.
With a heavy reward from the Persians, Ephialtes led them to the 300 Spartans of King Leonidas. He returned to his homeland of Malia (Malian Gulf) after many years, but was recognised by Athenades Trachinios, who killed him on the spot.
The definition of a traitor in ancient Greece was King Demaratus of Sparta, who was co-regent with wise Cleomenes who did everything to balance Persian influence.
Demaratus, although continuing the tradition of Chilon (one of the seven sages of antiquity), gave to the Persians and chose to shamelessly offer his advisory services to the Great King, the superpower of the time.
He ended up leaking military secrets to Xerxes.
The Spartan king even advised the Persians to occupy Kythera in order to defeat the Spartans, but his advice was not heeded.
The King of Sparta, Antalcidas, signed an infamous agreement with the Persians in Hephesus. With this treaty, all of Asia Minor, with the islands of Clazomenae and Cyprus, was recognised as subject to Persia, and all other Greek cities—so far they were not already under Persian rule—were to be independent, except Lemnos, Imbros, and Scyros, which were returned to the Athenians.
The terms were ratified by the city governments over the next year. The reassertion of Spartan hegemony over Greece by abandoning the Greeks of Aeolia, Ionia, and Caria has been called the "most disgraceful event in Greek history".