When was Constantine V born?

Emperor Constantine V was born in the summer of 718, however our only two texts that provide an approximate date of his birth diverge on the matter; mid-July according to Patriarch Nikephoros’ Breviarium, and early September according to Theophanes’ Chronographia. This paper first analyses the place of Constantine V’s birth in the two texts and argues that Theophanes moved the birth to attach it to the baptism episode, which was a separate event, effectively distorting the date of birth. The article also proposes that Theophanes had both practical and ideological reasons to do so and suggests that with the current state of the sources, evidence from the Breviarium is more likely to be closer to the actual date of birth of the infamous iconoclast emperor. Considering that the birth of an imperial heir had a legitimizing value, demonstrating the divine favour shown to the current ruler, and the importance of victory in 718, the last section of this paper further analyses whether the date-just before the retreat of the Arab army besieging Constantinople for about a year-may have played a role in Isaurian propaganda or in the memory of Constantine V as a triumphant ruler.