The title of this work refers to a fabled unit of Persian warriors from antiquity that remains a powerful symbol of national pride to this day. The main message of this book is that Iran's armed forces, as a potential military adversary of the United States, have demonstrated repeatedly over the course of more than 2,500 years that Iran should not be underestimated. The book illustrates the important factors that have given Iran's armed forces the phoenix-like regenerative abilities that have helped Iran survive the rise and fall of numerous empires and dynasties. This history also provides background on the nationalist, tribal, and religious heritages that motivate Iranian military personnel in order to help readers better understand Iran, its security outlook, and its armed forces. The book will conclude with an overview of Iranian military power today and the threat it poses to the United States and our Western and Middle Eastern allies. This is the only one-volume survey of Iran's military history available in English.