Thanks Ian!
I already asked Hagith Sivan on this issue. Her new book about Galla Placidia should be published any moment. She replied that Galla's date of birth remains very hypothetical and that she had no answer to my question.
Maybe not the early years of Galla Placidia herself was of influence on historical events, but that very period in 387-388, was the marriage she was born from of great importance for the motivation of Theodosius to battle with usurper Maximus instead of recognizing him as an emperor. Recently widowed (385) Theodosius was very enamoured and willing (Zosimus tells us) to the young Galla presented by her mother Justina (or was that war just a political and not a manupulated decision?). So what happened in the first years of their marriage?
388
The option of the birthdate of Galla Placidia in 388 could only be so if there wasn't a first born by the name of Gratian (as reported in Historia, 1985). If there was, 388 is not likely, ruling out the possibilty of her being a twin-brother of Gratian. Because of lack of documentation and research by contemporary historians, as Oost mentioned a bit irritated in 1965, I think this also could not be excluded. J.B. Bury must have a reason to ignore Gratian as an historical fact in his History of the late Roman Empire in 1923 using Gibbon's Decline and fall of the Roman Empire from 1776 and Zosimus Historia Nova from ca. 500 AD as sources. Maybe this event was not dug up again by scholars until 1985. By my knowlegde Oost also never mentioned Gratian in his article SOME PROBLEMS IN THE HISTORY OF GALLA PLACIDIA in 1965 nor in his 'Galla Placidia: a biographical essay' in 1968. So I add this son Gratian as a new aspect.
Evenso, because the marriage of Theodosius and Galla was in "early spring" of 387, March/ April that is, Gratian still could be born in the last days of 387 or the first months of 388. Theodosius was 41 by then and Galla 18 max. Then there are a few months for the newly weds and could 388 still be right.
So: the last months of 388.
389
If you consider that Theodosius left for a campaign to the West approximately in June or July 388 (fact is that he attended the battle of Sava on July 28th 388), there are even more months for the couple to determine Galla Placidia's birthdate in 389. Justina left Constantinople for Italy in 388 with her children, except Galla. Reason not to travel could be a pregnancy. Or to look after her stepsons Arcadius (10) and Honorius (3)? The first expelled her from the palace during the absence of Theodosius: Galla and a child. Was it Gratian or already Galla Placidia?
So 389 in March at the most is a possibility.
392
Theodosius returns to Constantinople in November 391. That makes July 392 the first occasion for her date of birth.
393
Because Galla dies at childbirth in 394 from their son John, the latest date could be March 393, calculating 9 months back.
Summary possible intervals:
1. End of 388 - March 389
Not likely, because sources like J.B. Bury, Gibbon and Zosimus state that the marriage was at the end of 387 (also Dictionary of Greek and Roman Biography and Mythology, 1849).
If you add up 9 months from Gratians birth, it's simply not possible.
Or Gratian is a lapsus historiae or Galla Placidia was her twin brother or the marriage was in the early spring. On what can we invalidate or verify these thesis?
2. July 392 - March 393.
This makes Galla Placidia 18 years old during the sack of Rome in August 410 by Alarik, being the key-figure for successory in the West for Honorius not able to have offspring.
Please comment on this!
Jeroen H de Lange,
Amsterdam