thumb|Bronze Statue of Demaratus in the Naples Museo Archeologico
Demaratus (Greek: Δημάρατος, Demaratos; Doric: Δαμάρατος, Damaratos) was a king of Sparta from around 515 BC to 491 BC. He was the 15th ruler of the Eurypontid dynasty and the firstborn son of King Ariston. During his reign, Demaratus is best known for his opposition to his co-ruler, King Cleomenes I of the Agiad dynasty. This rivalry ultimately led to his dethronement around 491 BC, following Cleomenes's accusations of illegitimacy and political maneuvering.
After his removal from power, Demaratus sought refuge in the Achaemenid Empire, where he was welcomed by King Darius I. He was granted land and cities in Asia Minor, integrating him into Persian society while retaining his influence. Demaratus served as an advisor to Xerxes I during the Second Persian invasion of Greece, providing strategic insights about Greek military tactics.
Early life
Demaratus was born into the Eurypontid dynasty of Sparta and was the firstborn son of King Ariston. His father's significance in the highly structured Spartan society meant Demaratus's firstborn status held considerable weight. According to Herodotus, Demaratus's birth was accompanied by a prophecy that suggested his future prominence and influence, with his name meaning "wished by the people." In Herodotus's writing, we see that King Ariston initially doubted his son's true parentage. "And he, after remembering when he had married the woman and counting out the months on his fingers, swore an oath: 'He could not be my own son!'"
Death and succession
thumb|upright=1.5|Coin of [[Prokles (Pergamon)|Prokles, brother and co-ruler of Eurysthenes, as Dynast of Teuthrania and Halisarna, and descendants of Demaratus, c. 400–399 BC. Teuthrania, Mysia. Laureate head of Apollo (left), head of Prokles (right) wearing Persian headdress.]]
There is no known year for Demaratus's death. Afterward, however, his sons, Eurysthenes and Prokles, succeeded him in ruling over the cities of Halisarna and Teuthrania in Aeolis. This succession maintained the connection between Demaratus's lineage and the city granted to him by the Persian king. His descendants ruled this area for approximately the next 80 years.
Demaratus's family continued to flourish in Asia as subjects of the Persians, and several of his descendants have been identified. One of them was likely Demaratus, the son of Gorgion, who was restored to Sparta in the early 3rd century BC and was, in turn, the putative great-grandfather of Nabis, the last king of Sparta (ruled 207–192).
Greek exiles in Achaemenid Empire
Demaratus was one of several Greeks aristocrats who took refuge in the Achaemenid Empire after reversals at home. Other famous cases were Themistocles and Gongylos. In general, they were generously rewarded by the Achaemenid kings, received land grants to support them and ruled over various cities in Asia Minor.