Placidia was born in Constantinople, the ancient city of Byzantium that was renamed for Emperor Constantine. She moved to Mediolanum (Milan) with her father and brothers when she was about eight years old. When her father died in 395, Honorius moved the court to Ravenna to take advantage of the city's impregnable position at the end of a long causeway. From Ravenna, Placidia traveled to Rome to assist in negotiations with Alaric. After she was taken hostage, the Goths marched to Calabria in southern Italy in order to reach Sicily and the grain fields of North Africa.
When Alaric died, Placidia and Ataulf led the Goths north to Gaul. They celebrated their marriage in Narbo, and settled in Barcino (Barcelona) on the eastern coast of Spain.