In August 1071, Byzantine Emperor Romanos IV Diogenes led a strong army to overturn the raids of the Seljuk Turks in the eastern heartland of the Empire. Guided by the Turkish sultan, Alp Arslan, Romanos was forced to fight with only half of his troops near Manzikert. By the end of the fateful day, a large part of the Byzantine army had been killed, the rest had scattered in flight, and the Emperor was captured. As a result, the eastern heart of the Empire was removed, and it was severely weakened, while Turkish power expanded rapidly, leading to Byzantine appeals for help from Western Europe, which inspired the First Crusade. This book places the battle in the context of the military history of the Byzantine Empire and the Islamic World (Arab and Seljuk Turks) up to the pivotal engagement at Manzikert in 1071, with particular emphasis on the origins, process, and outcomes of this battle. The composition, weapons, and tactics of the very different opposing armies are analyzed. The final chapter is dedicated to assessing the impact of Manzikert on the strategic position of the Byzantine Empire in Anatolia and the role of the battle as a _casus belli_ for the Crusades. Dozens of maps and battle diagrams support the clear text.