It was in 416 that Placidia returned to Ravenna.  In the following year Honorius gave her to Constantius, then his colleague in the consular office for the second time.  The marriage ceremony of very great splendour took place in Ravenna; and in the same year was born of that marriage Honoria, who was to offer herself to Attila, and in 419 Valentinian, one day to be emperor.

That marriage soon had the result Constantius had intended.  In 421 Honorius was compelled to associate him with himself on the imperial throne and to give to Placidia the title of Augusta.  The new emperor, however, survived his elevation to the throne but seven months and once more Placidia was a widow.  Her life, never a happy one, if we except the few years in which she was the wife of Ataulfus, whom she seems really to have loved, became unbearable after the death of Constantius.  At the mercy of her brother who was fast sinking, at the age of thirty-nine, into a vicious and idiotic senility, she, always a sincere Catholic in spite of her romantic marriage with the Arian Ataulfus, seems to have been forced into a horrible intimacy with him; at least we know that he obliged her to receive his obscene kisses, even in public, to the scandal and perhaps the amusement of that corrupt society.  And then suddenly her brother’s dreadful love seems to have turned to hate and she is a fugitive again with her two children at the court of her nephew Theodosius II. at Constantinople.  In the very year of her flight Honorius died and the throne of the West was vacant.

It was filled by the obscure civil servant Joannes, the chief of the notaries, the creature of some palace intrigue.  But such a choice could not be tolerated by Theodosius, who immediately confirmed Placidia in her title of Augusta, which had not before been recognised at Constantinople, and accepted Valentinian, whose title was Nobilissimus, as the heir to the western throne, giving him the title of Caesar.  To suppress the usurper Joannes, Theodosius despatched an army to bring Placidia and her children to Ravenna.  After a short campaign in northern Italy, by a miracle, according to the contemporary historian Socrates, the troops of Theodosius arrived before Ravenna.  “The prayer of the pious emperor again prevailed.  For an angel of God, under the semblance of a shepherd, undertook the guidance of Aspar and his troops, and led them through the lake near Ravenna.  Now no one had ever been known to ford that lake before; but God then caused that to be possible which before had been impossible.  But when they had crossed the lake, as if going over dry land, they found the gates of the city open and seized the tyrant Joannes."[1]

[Footnote 1:  Socrates, vii. 23.  Cf.  Hodgkin, op cit. i. 847.]

So the Augusta with the young Caesar and her daughter Honoria entered Ravenna, to reign there, first as regent and then as the no less powerful adviser of her son, for some twenty-five years.