Cyrus was also the name of a
Persian prince at the end of the fifth century B.C..
Cyrus the younger was the second son of Darius II. In 408 B.C., at the age of 16, he was assigned command of the entire west coast of the Persian Empire. Here he became good friends with Lysander the Spartan general, at the time Sparta was approaching Persia for money and Cyrus was instrumental in seeing that they got it. He was not exactly subtle about his desire for the throne, when in 406 B.C. he executed two of his cousins for not showing him the respect deserved by a king. He was then recalled by his father to explain his action but also to visit his father who was ill at the time.
In 404 B.C. Darius II died and his son ascended the throne assuming the name Artaxerxes II. Cyrus with the aid of his mother returned to his satrapy and prepared to raise rebellion against his brother. In 401 B.C. he revolted with the armies he had raised in Asia Minor, along with a large number of Greek mercenaries and aid from Sparta. He engaged the army of his brother at the battle of Cunaxa. In the battle Cyrus was killed and most of his army was defeated, however the Greek mercenaries on the right wing easily defeated Artaxerxes' left wing and then attacked again running off the Persians despite the remainder of Cyrus' army fleeing the field. These Greek mercenaries having lost their commanders elected Xenophon to lead them all the way to Byzantium, the story of this march is told in Xenophon's anabasis.
The reason Cyrus failed was a political one, he had failed to secure the support of the Persian nobility that he needed for his campaign to succeed. When he died at the age of 23 he had already been responsible for the Spartan victory in the second Peloponnesian War and for Sparta's war with Persia that arose over the help they gave him.