 The date of their creation is also uncertain.For most of the 20th century, the establishment of the themes was attributed to the Emperor Heraclius (r. 610–641), during the last of the Byzantine–Sassanid Wars.Most notable amongst the supporters of this thesis was George Ostrogorsky who based this opinion on an extract from the chronicle of Theophanes the Confessor mentioning the arrival of Heraclius "in the lands of the themes" for the year 622.