[1] The Empire was obligated by the 188 BC Treaty of Apamea, signed after King Antiochus III lost a war against the Romans, to send a hostage to Rome; at first, Antiochus' uncle Antiochus IV was sent as a hostage.

After Antiochus III's death in 187 BC, Seleucus IV replaced his brother Antiochus IV with his own eldest son and heir Demetrius I, since Rome considered it important that a son of the reigning king be a hostage.

[2] The death of Seleucus IV in 175 BC and the presence of Demetrius I in Rome led to the young Antiochus' proclamation as king,[3] but the minister Heliodorus who probably killed Seleucus IV held the real power.

[1] Antiochus IV soon arrived in Syria and proclaimed himself a co-ruler, in a succession that was illegal.

[3] Antiochus IV disposed of Heliodorus and kept his nephew in the shadow.