After the death of his predecessor Honorius, the nephew of the eastern emperor, he was pushed forward as a successor by Castinus, patricius and magister militum (commander-in-chief) of the western army.

[2] In 424, diplomatic tensions between the two imperial halves continued when Theodosius named his nephew Valentinian as Caesar of the western part with his mother Placidia as Augusta.

[6] Before this help arrived, Theodosius decided to take action and ordered his chief commander-in-chief magister militum Ardaburius to overthrow Joannes Reijn.

John of Antioch, on the other hand, argues that a shepherd led the army of Aspar safely through the swamps that protected the city and that local allies opened the gate for them.

According to Stewart East West Ardaburius, during his captivity, he persuaded a number of Western Roman officers to commit a coup against Emperor Joannes, which they succeeded in doing.