The reign of Heraclius (AD 610-641) was, I think it's fair to say, the most dramatic of any Roman or Byzantine emperor, with initial disasters followed by a spectacular recovery, followed by renewed disasters. It has as good claim as any to mark the transition from late antique East Rome to medieval Byzantium.

The life of Heraclius, then, is promising material for a biography, although that promise is tempered by the sources available not being all that we may wish. Kaegi pulls it off quite well, managing to discuss the gaps and uncertainties in the sources without bogging down the narrative unduly. The style is unexpectedly conversational for what's essentially an academic work, and there's some unnecessary repetitions, but those are minor faults.

Sadly, this book is he best we have. Sources are sparse and compared to the amount normally associated with the genre. The acidents of time have dispersed the official material, and the general chronicles and hagiography consulted are seldom presenting anything but a stock figure usable for literary convention. Part of the time I found myself saddened, as there must have been more to the man than what we can prove. The Armenian History by Sebeos, Michael the Syrian, and the Hagiographies are of more use than any Arabic sources, where he is nothing more than the stock figure of blind resistance to the obvious will of Allah.
Kaegi believes far more in Heraclius as an astute politician, than a brilliant soldier. It seems that Heraclius , manipulated his Persian opponents weaknesses to relieve his empire of a very serious invasion. But when the Arabs suddenly injected themselves into history, neither of the more settled powers had any handle on the crisis. But Heraclius' empire survived, though badly reduced, while the Persians went into "A bit of a decline", for three hundred years. Kaegi has the reasons marshalled quite well.
It is a useful book, not the least part being an exploration of the kind of lemonade that can be made from the very few lemons presented. But it's not a lively read. ( )