This book examines the use of Christian relics as protective amulets, emblems, and talismans in war and military contexts in the Eastern Roman Empire (ca. 310–1204). For centuries, Christians have venerated the mortal remains of holy figures and objects sanctified by contact with them as relics and believed in their miraculous powers. This book explores how the belief in protective relics and associated cultural practices emerged in Late Antiquity and developed over the Middle Ages, with a focus on Constantinople and the Eastern Mediterranean. It proposes a chronology for the development of these beliefs and associated practices, reassesses the ritual and processional use of relics, and analyzes how the Byzantine imperial elite deployed relics to build social cohesion, authority, and legitimacy.