In the autumn of 602 CE, a mutinous Balkan army raised a junior officer named Phocas to the throne of the Eastern Roman Empire. Eight years later, a rebel fleet sailed from the exarchate of Africa, decorated with icons of the Virgin Mary, to take that throne back. What happened in between changed the shape of the medieval world. The Purple and the Sword is the definitive narrative history of the Heraclian revolt - the conspiracy hatched in Carthage, the two-pronged military campaign that seized Egypt and the Mediterranean simultaneously, the betrayal at Constantinople's heart, and the coronation that established a dynasty governing Byzantium for a century. It is also the story of consequences: the Persian war that the revolt helped to escalate, the fall of Jerusalem and the loss of the True Cross, the extraordinary holy war counter-offensive that recovered everything - and the Islamic expansion that undid it within a decade. Drawing on Byzantine, Coptic, Syriac, and Armenian sources, Demetrius O'Kelly weaves military history, political theology, and numismatic strategy into a narrative of singular scope and human depth. From the exarchal palace in Carthage to the deck of a flagship at the Golden Horn, this is the story of how an empire was lost, remade, and permanently transformed by the most consequential decade in its long history.