Remembered as an exemplar of cold-blooded realpolitik, the Byzantine Empire actually pioneered the combination of military and religious fervor known as holy war, according to this colorful history. Regan, a historian and author of Great Military Blunders, covers some 800 years of Byzantine history, from the founding of Constantinople to the arrival of Western crusaders in the 12th century to take up the war against Islam. He focuses on the 7th century emperor Heraclius, celebrated for his knightly duels against enemy champions, who used religious appeals to build an army of "fanatics, zealots, martyrs and holy warriors" to defeat the Zoroastrian Persian Empire, recapture Jerusalem and recover the True Cross, Christendom's holiest relic. Heraclius's ideal of holy war devolved into "ersatz crusades"-one campaign against the Muslims sought to retrieve a holy towel imprinted with Christ's face-overshadowed by the endless factional intrigue, civil wars and intra-Christian schisms and persecutions that made the Byzantines their own worst enemies, but Regan argues for its lasting historical impact. The Byzantine's innovative fusion of military and religious enthusiasm, he speculates, may have influenced the development of the Muslim jihad that would soon overrun much of the Empire, and became a precedent for the Western Crusades. Regan makes the most of skimpy sources to draw a lucid portrait of the crazed piety, back-stabbing politics, chaotic battles and brutal massacres that characterize this period. Writing in an engaging style without academic jargon, he brings to life a lurid but neglected age that reverberates into our own. Photos. (Apr.) Copyright 2003 Reed Business Information.