After the death of their father, Demetrius III took control of Damascus while his brother Seleucus VI prepared for war against Antiochus IX, who occupied the Syrian capital Antioch.

He attempted to appease the public by promoting the importance of the local Semitic gods, and he may have given Damascus the dynastic name Demetrias.

The Seleucid Empire, based in Syria, disintegrated in the second century BC as a result of dynastic feuds and Egyptian interference.

[note 2][13] Following the death of his brother, Antiochus IX took the Syrian capital, Antioch,[14] while Seleucus VI, established in Cilicia, prepared for war against his uncle.

[22] Historian Kay Ehling noted that Josephus's account is a condensed summary and the actual course of events surrounding Demetrius III's seizure of power needs to be reconstructed.

[42] Josephus is the only source for the nickname; in the view of historians David Levenson and Thomas Martin, Eucaerus should not be used to refer to Demetrius; instead, Akairos, or one of his official epithets should be used.

[note 7][59][60] Damascene coins mention the city as "holy"; it must have been a privilege bestowed upon it by Demetrius III who possibly also conferred the right of asylum on his capital.

[68] As was typical for a Seleucid king, Demetrius III aimed to acquire as much territory as possible and sought to expand his domains in Syria.

[note 9][72] Gadara was of great strategic importance for Demetrius III as a major military hub for operations in the south; controlling it was vital to the war effort against the Judaeans.

[75] In 94 BC, Seleucus VI was driven out of the capital by Antiochus X;[48] the former escaped to the Cilician city of Mopsuestia where he perished during a local uprising.

[83] It is possible that either the Judaeans or the Nabataeans took advantage of Demetrius III's departure to help his brother and occupied the city;[81] the King regained Damascus in 221 SE (92/91 BC).

[82] Those traditional dates are hard to justify; using a methodology based on estimating the annual die usage average rate (the Esty formula), Hoover proposed the year 224 SE (89/88 BC) for the end of Antiochus X's reign.

[87] Following the defeat of Alexander Jannaeus at the hands of the Nabataeans, Judaea was caught in a civil war[72] between the king and a religious group called the Pharisees.

[88] According to Josephus, Alexander Jannaeus' opponents persuaded Demetrius III to invade Judaea as it would be conquered easily owing to the civil war.

[89] Josephus gave two accounts regarding the numerical strength of Demetrius III; in Antiquities of the Jews, the Syrian king had 3,000 cavalry and 40,000 infantry.

[note 12] This increase indicates that Demetrius was securing the necessary funds for his campaign, making 89 BC more likely as the date of the invasion.

Following this failed attempt, the two kings engaged in battle; Demetrius III lost many troops but decimated Alexander Jannaeus's mercenaries and gained victory.

[103] Probably in 88 BC, Antiochus X died while fighting the Parthians, and this must have forced Demetrius III to rush north and fill the power vacuum before Philip I.

[89] During this conflict, which is datable to 225 SE (88/87 BC), soldiers from Antioch were mentioned for the first time in the ranks of Demetrius III, indicating that he took control of the Syrian capital in this year.

[note 17][95] No bronze coinage was minted in the name of Demetrius III in Antioch as the city began issuing its own civic bronze coins in 221 SE (92/91 BC); Demetrius III issued silver coins in the Syrian capital as silver coinage remained a royal prerogative.

[103] Philip I's ally, Straton, the tyrant of the city, called on Aziz, an Arab phylarch (tribal leader), and the Parthian governor Mithridates Sinaces for help;[109] the allies' archery drove Demetrius III to take cover in his camp, where he was besieged and eventually surrendered after thirst took its toll on his men.

[111][112] Demetrius III was probably childless;[113] in Damascus, he was succeeded by Antiochus XII, whose first coin was minted in 226 SE (87/86 BC), indicating an immediate succession.