The Greek researcher Herodotus of Halicarnassus (c.480 - c.425) is the author of the entertaining Histories, in which he describes the rise of the Achaemenid Empire and the conflict between the Greeks and Persians in 480 BCE. His account contains much other information that is not directly relevant to his main theme, such as the story of Dorieus.
This was a Spartan prince who founded two colonies in oversea countries in the years 515-510 BCE, Cinyps in Libya and Heraclea on Sicily. According to Herodotus, the motor behind Dorieus' activities was the fact that he did not like his brother Cleomenes, who had been made king after the death of their father Anaxandridas II. The truth may be that Cleomenes, one of the most energetic rulers of his age, took the real initiative for the Spartan colonization and send his brother away on this honorable mission.
This translation of Herodotus' Histories 5.42-44, 46-48 was made by G. C. Macaulay. Some changes have been made.
Herodotus about Dorieus
[5.42] Cleomenes, it is said, was not quite in his right senses but on the verge of madness, while Dorieus was of all his equals in age the first, and felt assured that he would obtain the kingdom by merit. [...] However, when [king] Anaxandridas died, the Spartans followed the usual custom and established the eldest, namely Cleomenes, upon the throne. Dorieus, indignant and thinking it was wrong if he should be a subject of Cleomenes, asked the Spartans to give him a company of followers and led them out to found a colony, without either inquiring of the Oracle at Delphi to what land he should go to make a settlement, or doing any of the things which are usually done; but being vexed he sailed away with his ships to Libya [...].
Having arrived at Cinyps, he made a settlement in the fairest spot of all Libya, along the banks of the river; but in the third year he was driven out from thence by the Macae [a native tribe], Libyans, and Carthaginians, and returned to Peloponnese.
[5.43] Then Antichares, a man of Eleon, gave him counsel out of the oracles of Laïos to make a settlement at Heracleanote[There was a town named Heraclea, "the city of Heracles", in the southwestern part of Sicily. It may originally have been a Carthaginian settlement (their god Melqart being often identified with the Greek Heracles). In old stories, it was maintained that Heracles had visited the western parts of the Mediterranean, looking for the cattle of Geryon, which was sometimes explained as a conquest.] in Sicily, saying that the whole land of Eryxnote[Eryx was the name of a high mountain in western Sicily, close to the Carthaginian settlements. "Conquering the land of Eryx" must have been the equivalent of "expelling the Carthaginians from Sicily once and for all".] belonged to the Heraclids, since Heracles himself had won it. Hearing this, Dorieus went forthwith to Delphi to inquire of the Oracle whether he would be able to conquer the land to which he was setting forth; and the Pythian prophetess replied to him that he would conquer it. Dorieus therefore took with him the armament which he conducted before to Libya, and voyaged along the coast of Italy.
[5.44] Now at this time, the men of Sybaris [in southern Italy] said that they and their king Telys were about to make an expedition against Croton, and the men of Croton being exceedingly alarmed asked Dorieus to help them and obtained their request. So Dorieus joined them in an expedition against Sybaris and helped them to conquer Sybaris. This is what the men of Sybaris say of the doings of Dorieus and his followers; but those of Croton say that no stranger helped them in the war against the Sybarites except Callias alone, a diviner of Elis.
[5.46] Now there sailed with Dorieus others also of the Spartans, to be co-founders with him of the colony, namely Thessalus and Paraebates and Celeas and Euryleon; and these when they had reached Sicily with all their armament, were slain, being defeated in battle by the Phoenicians [Carthaginians] and the men of Segesta; and Euryleon only of the co-founders survived this disaster.note[This includes Dorieus.]
This man collected the survivors of the expedition, took possession of Minoa (a colony of Selinus), and he helped to free the men of Selinus from their despot Peithagoras. Afterwards, when he had deposed him, he laid hands himself upon the despotism in Selinus and became tyrant there, though but for a short time; for the men of Selinus rose in revolt against him and slew him, notwithstanding that he had fled for refuge to the altar of Zeus on the market.
[5.47] In this manner Dorieus ended his life: but if he had endured to be a subject of Cleomenes and had remained in Sparta, he would have been king of Sparta; for Cleomenes reigned no very long time, and died leaving no son to succeed him but a daughter only, whose name was Gorgo.note[She married to Leonidas, who fell during the battle of Thermopylae. She, or someone very close to her, may have been one of Herodotus' informers.]