As a result of these victories, Attalus gained control over all of Seleucid Asia Minor north of the Taurus Mountains. He was able to hold on to these gains in the face of repeated attempts by Seleucus III Ceraunus, eldest son and successor of Seleucus II, to recover the lost territory, culminating in Seleucus III himself crossing the Taurus, only to be assassinated by members of his army in 223 BC. Achaeus, who had accompanied Seleucus III, assumed control of the army. He was offered and refused the kingship in favor of Seleucus III's younger brother Antiochus III the Great, who then made Achaeus governor of Seleucid Asia Minor north of the Taurus. Within two years Achaeus had recovered all the lost Seleucid territories, shut up Attalus within the walls of Pergamon, and assumed the title of king.