Syennesis: title of the native king of Cilicia, whose palace was at Tarsus. The Luwian word suuannassai means "belonging to the dog", a title that is well attested although its meaning remains unclear. Three leaders with this name are known.
According to the Greek researcher Herodotus of Halicarnassus (fifth century BCE), Syennesis of Cilicia and Labynetus of Babylon negotiated a peace treaty between king king Alyattes of Lydia and king Cyaxares of Media.
War broke out between the two countries and continued for five years, during which both the Lydians and Medes won a number of victories. On one occasion they had an unexpected battle in the dark, an event which occurred after five years of indecisive warfare. The two armies had already engaged and the fight was in progress, when the day was suddenly turned into night. [...] Both Lydians and Medes broke off the engagement when they saw this darkening of the day; they were more anxious than they had been to conclude peace, and a reconciliation was brought about by Syennesis, a Cilician, and Labynetus of Babylon, who were the men responsible both for the pact to keep the peace and for the exchange of marriages between the two kingdoms. They persuaded Alyattes to give his daughter Aryenis to Astyages, son of Cyaxares - knowing that treaties seldom remain intact without powerful sanctions.note[Herodotus, Histories 1.74.]
This is all that is known about this first Syennesis. We do not even know his real name. The Labynetus mentioned in this fragment probably is the later king of the Babylonian Empire, Nabonidus (r.556-539). The solar eclipse can be dated to May 28, 585 BCE.
Appuašu is mentioned as king of Cilicia in a Babylonian chronicle that refers to a campaign of king Neriglissar in 557/556 (ABC 6). He must have been the son of Syennesis I and will have used the same title, although this is not mentioned. Although the Babylonian army reached Cilicia and crossed the Taurus mountain range, Appuašu was not defeated.
It is possible that Neriglissar attacked Cilicia because Appuašu was a vassal king of the Median empire, the rival of Babylonia. We can not be certain about it. When the Medes were defeated by the Persian leader Cyrus the Great, Appuašu may have tried to regain his independence, but he was unsuccesful. He probably became a vassal king of Persia in c.546, after Cyrus the Great had conquered Croesus of Lydia.
Oromedon is mentioned as the father of Syennesis II. If he was king of Cilicia, he must have used the title Syennesis, but this is not mentioned in our sources.
This Cilician ruler was the son of Oromedon and was probably the grandson of Appuwašu. He is mentioned as one of the commanders in the Persian navy during Xerxes' invasion of Greece (480 BCE). He married his daughter to Pixodarus, a Carian leader.
Syennesis III was probably the grandson of Syennesis II. He was married to Epyaxa; in 401, the couple supported the revolt of Cyrus the Younger against his brother Artaxerxes II Mnemon. This was sound policy, because otherwise, Cilicia would have been looted by the rebel army. However, after the defeat of Cyrus at Cunaxa, Syennesis' position was difficult. Most scholars assume that this behavior marked the end of the independence of Cilicia. After 400, it became a normal satrapy.