More Merovingian- Kingdom of Soissons

[AMELIANVS]

Didn't one Legion survive until almost 900 AD? IV Parthica I think?

You probably have Victores and Theodosiaci on mind.They are mentioned for the last time around 950 AD(being mentioned in action in previous century as well).

IV.Parthica is mentioned for the last time in 586 and V.Macedonica in early 7th century.