Book excerpt: War of the Three Gods is a military history of the first half of seventh century, with heavy focus on the reign of the Eastern Roman Emperor Heraclius (AD 610-641). This was a pivotal time in world history as well as a dramatic one. The Eastern Roman Empire was brought to the very brink of extinction by the Sassanid Persians, before Heraclius managed to inflict a crushing defeat on the Sassanids with a desperate, final gambit. His conquests were short-lived, however, for the newly-converted adherents of Islam burst upon the region, administering the coup de grace to Sassanid power and laying siege to Constantinople itself to usher in a new era. ??Peter Crawford skilfully narrates the three-way struggle between the Christian Byzantine, Sassanid Persian and Islamic empires, a period peopled with fascinating characters, including Heraclius, Khusro II and the Prophet Muhammad himself. Many of the epic battles and sieges are described in as much detail as possible including Nineveh, Yarmouk, Qadisiyyah and Nihawand, Jerusalem and Constantinople. The strategies and tactics of these very different armies are discussed and analysed, while maps allow the reader to place the events and follow the varying fortunes of the contending empires. This is an exciting and important study of a conflict that reshaped the map of the world.