Galla Placidia herself was now forced from the Western Empire.
Though the motivation for this remains unclear, the public issue was the increasingly scandalous public caresses she received from her own brother Honorius—this at least was the interpretation of Olympiodorus of Thebes, a historian used as a source by Zosimus, Sozomen and probably Philostorgius, as J.F. Matthews has postulated.
Gibbon had a different opinion: "The power of Placidia; and the indecent familiarity of her brother, which might be no more than the symptoms of a childish affection, were universally attributed to incestuous love."


According to Gibbon, "On a sudden, by some base intrigues of a steward and a nurse, this excessive fondness was converted into an irreconcilable quarrel: the debates of the emperor and his sister were not long confined within the walls of the palace; and as the Gothic soldiers adhered to their queen, the city of Ravenna was agitated with bloody and dangerous tumults, which could only be appeased by the forced or voluntary retreat of Placidia and her children.
The royal exiles landed at Constantinople, soon after the marriage of Theodosius, during the festival of the Persian victories.
They were treated with kindness and magnificence; but as the statues of the emperor Constantius had been rejected by the Eastern court, the title of Augusta could not decently be allowed to his widow."
The passage places the arrival of Placidia and her children after the marriage of Theodosius II to Aelia Eudocia, known to have occurred on June 7, 421.
The "Persian victories" mentioned were probably victory celebrations over the brief Roman–Sasanian War (421–422) under the respective leadership of Theodosius II and Bahram V of the Sasanian Empire.

The general Ardaburius operated in Arzanene and gained a victory, autumn 421, which forced the Persians to retreat to Nisibis, which Ardaburius then besieged.
He raised the siege on the arrival of an army under Bahram V, who proceeded to attack Resaina.
Meanwhile the Saracens of Hira, under Al‑Mundhir, were sent to invade Syria, and were defeated by Vitianus.
During the peace negotiations the Persians attacked the Romans and were defeated by Procopius, son-in‑law of Anthemius (Socrates, VII.18, 20).
The Empress Eudocia celebrated the war in a poem in heroic metre (ib.
21)."

 The "Saracens of Hira" were the Lakhmids of al-Hirah, a pre-Islamic Arab state that was located in what is now Iraq.

On August 15, 423, Honorius died of edema, perhaps pulmonary edema.
With no member of the Theodosian dynasty present at Ravenna to claim the throne, Theodosius II was expected to nominate a Western co-emperor.
However, Theodosius hesitated and the decision was delayed.
Taking advantage of the power vacuum, Castinus the Patrician proceeded to become a kingmaker.
He declared Joannes, the primicerius notariorum "chief notary" (the head of the civil service), to be the new Western Roman Emperor.
Among their supporters was Flavius Aetius.
Aetius was a son of Flavius Gaudentius, magister militum, and Aurelia.
Joannes' rule was accepted in the provinces of Italia, Gaul and Hispania, but not in the province of Africa.

Theodosius II reacted by preparing Valentinian III for eventual promotion to the imperial office.
In 423/424, Valentinian was named nobilissimus.
In 424, Valentinian was betrothed to Licinia Eudoxia, his first cousin once removed.
She was a daughter of Theodosius II and Aelia Eudocia.
The year of their betrothal was recorded by Marcellinus Comes.
At the time of their betrothal, Valentinian was approximately four years old, Licinia only two.
Gibbon attributes the betrothal to "the agreement of the three females who governed the Roman world", meaning Placidia and her nieces Eudocia and Pulcheria.
In the same year, Valentinian was proclaimed a Caesar in the Eastern court.

The campaign against Joannes also started in the same year.
Forces of the Eastern Roman army gathered at Thessaloniki, and were placed under the general command of Ardaburius, the victorious general of the Roman-Persian War.
The invasion force
Galla Placidia herself was now forced from the Western Empire. Though the motivation for this remains unclear, the public issue was the increasingly scandalous public caresses she received from her own brother Honorius—this at least was the interpretation of Olympiodorus of Thebes, a historian used as a source by Zosimus, Sozomen and probably Philostorgius, as J.F. Matthews has postulated. Gibbon had a different opinion: "The power of Placidia; and the indecent familiarity of her brother, which might be no more than the symptoms of a childish affection, were universally attributed to incestuous love."

According to Gibbon, "On a sudden, by some base intrigues of a steward and a nurse, this excessive fondness was converted into an irreconcilable quarrel: the debates of the emperor and his sister were not long confined within the walls of the palace; and as the Gothic soldiers adhered to their queen, the city of Ravenna was agitated with bloody and dangerous tumults, which could only be appeased by the forced or voluntary retreat of Placidia and her children. The royal exiles landed at Constantinople, soon after the marriage of Theodosius, during the festival of the Persian victories. They were treated with kindness and magnificence; but as the statues of the emperor Constantius had been rejected by the Eastern court, the title of Augusta could not decently be allowed to his widow." The passage places the arrival of Placidia and her children after the marriage of Theodosius II to Aelia Eudocia, known to have occurred on June 7, 421. The "Persian victories" mentioned were probably victory celebrations over the brief Roman–Sasanian War (421–422) under the respective leadership of Theodosius II and Bahram V of the Sasanian Empire.
The general Ardaburius operated in Arzanene and gained a victory, autumn 421, which forced the Persians to retreat to Nisibis, which Ardaburius then besieged. He raised the siege on the arrival of an army under Bahram V, who proceeded to attack Resaina. Meanwhile the Saracens of Hira, under Al‑Mundhir, were sent to invade Syria, and were defeated by Vitianus. During the peace negotiations the Persians attacked the Romans and were defeated by Procopius, son-in‑law of Anthemius (Socrates, VII.18, 20). The Empress Eudocia celebrated the war in a poem in heroic metre (ib. 21)."
 The "Saracens of Hira" were the Lakhmids of al-Hirah, a pre-Islamic Arab state that was located in what is now Iraq.
On August 15, 423, Honorius died of edema, perhaps pulmonary edema. With no member of the Theodosian dynasty present at Ravenna to claim the throne, Theodosius II was expected to nominate a Western co-emperor. However, Theodosius hesitated and the decision was delayed. Taking advantage of the power vacuum, Castinus the Patrician proceeded to become a kingmaker. He declared Joannes, the primicerius notariorum "chief notary" (the head of the civil service), to be the new Western Roman Emperor. Among their supporters was Flavius Aetius. Aetius was a son of Flavius Gaudentius, magister militum, and Aurelia. Joannes' rule was accepted in the provinces of Italia, Gaul and Hispania, but not in the province of Africa.
Theodosius II reacted by preparing Valentinian III for eventual promotion to the imperial office. In 423/424, Valentinian was named nobilissimus. In 424, Valentinian was betrothed to Licinia Eudoxia, his first cousin once removed. She was a daughter of Theodosius II and Aelia Eudocia. The year of their betrothal was recorded by Marcellinus Comes. At the time of their betrothal, Valentinian was approximately four years old, Licinia only two. Gibbon attributes the betrothal to "the agreement of the three females who governed the Roman world", meaning Placidia and her nieces Eudocia and Pulcheria. In the same year, Valentinian was proclaimed a Caesar in the Eastern court.
The campaign against Joannes also started in the same year. Forces of the Eastern Roman army gathered at Thessaloniki, and were placed under the general command of Ardaburius, the victorious general of the Roman-Persian War. The invasion force
Galla Placidia