Although Roman centurions appear at crucial stages in the Gospel of Luke and the Acts of the Apostles, the significance of the centurion's office for the development of Luke's story has not been adequately researched. To fill in that void, this study engages the relevant Greco-Roman and Jewish sources that reflect on the image of the Roman military and applies the findings to the analysis of the role of the Roman centurion in the narrative of Luke-Acts. It argues that contemporary evidence reveals a common perception of the Roman centurion as a principal representative of the Roman imperial power, and that Luke-Acts employs centurions in the role of prototypical Gentile believers in anticipation of the Christian mission to the Empire. Chapter 1 outlines the current state of the question. Chapter 2 surveys the background data, including the place of the centurion in the Roman military organization, the role of the Roman army as the basis of the ruling power, the army's function in the life of the civilian community, Luke's military terminology, and the Roman military regiments in Luke-Acts. Chapter 3 reviews Greco-Roman writings, including Polybius, Julius Caesar, Sallust, Livy, Velleius Paterculus, Tacitus, Appian, Cornelius Nepos, Plutarch, Suetonius, Plautus, Cicero, Virgil, Horace, Petronius, Quintilian, Epictetus, Juvenal, Fronto, Apuleius, as well as non-literary evidence. Chapter 4 engages the Jewish witnesses, including 1 Maccabees, the Dead Sea Scrolls, Jewish pseudepigrapha, Philo, Josephus, Talmudic sources, and non-literary sources. Chapter 5 examines the relevant accounts of Luke-Acts, focusing on Luke 7:1-10 and Acts 10:1-11:18. The Conclusion reviews the findings of the study and summarizes the results.