Galla (5) Placidia, daughter of Theodosius I., by his second wife Galla. When in 410 Rome was captured by Alaric, Placidia was taken prisoner, but was treated with great respect (Olympiod. ap. Phot. Biblioth. lxxx.; Zos. Hist. vi. 12), and in Jan. 414, at Narbona in Gaul, married Ataulphus, who had succeeded his uncle Alaric. After the death of Ataulphus, Placidiareturned to Italy, a.d. 416, and dwelt with her paternal uncle Honorius, at Ravenna. In Jan. 417 she married Constantius. By him she had two children, Valentinian and Honoria (Olympiod. u.s. ) Her influence over Constantius was soon shewn in his active persecution of the Pelagians (Prosp. Chron. s.a. 418), when, in Feb. 421, Honorius admitted Constantius to a share of the empire. On Sept. 11, 421, Constantius died. Placidia again took up her abode with Honorius at Ravenna, but their mutual affection being replaced by bitter hate, which occasioned serious disturbances in the city, she and her children were sent to Theodosius II. at Constantinople (Olympiod. u.s. ). On the death of Honorius in Aug. 423, Theodosius declared for Valentinian. Valentinian being but a child, the authority of Placidia was now supreme, and among her first acts was the issue of three edicts in rapid succession for the banishment of all "Manicheans, heretics, and schismatics, and every sect opposed to the Catholic faith" (Cod. Theod. XVI. v. 62, July 17; ib. 63, Aug. 4; ib. 64, Aug. 6, 425, all dated from Aquileia), meaning especially the adherents of the antipope Eulalius, who were still numerous in Rome. These edicts were soon followed by another of great severity, directed against apostates ( Cod. Theod. XVI. vii. 8, Apr. 7, 426).
In 427 the machinations of Aetius put Placidia in conflict with her tried friend Boniface, count of Africa, who, in despair, appealed for help to the Vandals, and Africa was overrun by their forces. Placidia explained matters to Boniface, and urged him to do his best to repair the injury which the empire had sustained. But it was too late; the Vandals were masters of the country, and Africa was lost (Procop Bell. Vandal. i. 4; Augustine, Ep. 220; Gibbon, c. xxxiii.).
In 449 Placidia was at Rome with Valentinian. The legates of Leo had just returned from the Robber Council of Ephesus. Leo bitterly bewailed the doings of that assembly to Placidia, who immediately wrote to Theodosius and his sister Pulcheria, intreating them to interfere in defence of the faith of their ancestors and to procure the restoration of Flavian, the deposed bp. of Constantinople (Conc. Chalced., pt. i. Ep. 26, 28, 30; Labbe, iv. 53, 55, 58). She died soon afterwards at Rome, and was buried at Ravenna (Idatius, Chr. s.a.; Gibbon, u.s. ).