Claudius Lysias is a figure mentioned in the New Testament book of the Acts of the Apostles. According to Acts 21:31-24:22, Lysias was a Roman tribune and the commander (chiliarch) of the Roman garrison ("cohort" Acts 21:31) in Jerusalem.
Claudius Lysias is called "the tribune" (in Greek χιλίαρχος, chiliarch) 16 times within Acts 21-24 (21.31-33, 37; 22.24, 26-29; 23.10, 15, 17, 19, 22; 24.22).
The Greek term χιλίαρχος is said to be used to translate the Roman tribunus militum (following Polybius), and also for the phrase tribuni militares consulari potestate (Plutarch). The responsibilities of a χιλίαρχος were as a "commander of a thousand men". Essentially, Claudius Lysias is "a high-ranking military officer in charge" of anywhere from 600 to 1,000 men, and this appears to be the case for it is said that his command was over a "cohort" (σπεῖρα, speira) in Jerusalem which is "the tenth part of a Roman legion having about 600 men" (Acts 21:31).
Claudius Lysias' complete description as found in the New Testament book of the Acts of the Apostles is "the tribune of the cohort" in Jerusalem, which resided in nearby "barracks" (Acts 21.34, 37; 22.24, 23.10, 16, 32). It takes ten cohorts to make up a legion, and each legion had six tribunes with a thousand men ("soldiers and centurions" Acts 21:32) under his command if the cohort was full; consequently, Claudius Lysias was a part of a larger military force. The exact numbers in his cohort may never be known, however he had sufficient men to spare two centurions, two hundred soldiers, seventy horsemen, and two hundred spearmen to accompany Paul to Caesarea Acts 23:23-24. Furthermore, when the security detail arrives before Antipartis (Acts 23:31), Claudius Lysias allows for the seventy horsemen to go on with him and Paul to Caesarea, the headquarters of the Procurator Felix (Acts 23:32-35).