Q. How and when did polygamy become illegal in the Roman Empire? I have heard that it was Flavius who made it illegal and not Justinian.
We have quite a bit more research to do on this subject. There is one school which maintains that Rome tried to ban polygamy as early as the beginning of the fifth century under the rule of Flavius Honorius (see picture) but I have not, as yet, seen the evidence for this. Until there is more data we shall stick with the Justinian edict of the 6th century.