Quaternion

A quaternion (Greek tetradion, meaning a group of four) was a squad of four Roman soldiers assigned as a guard unit. In Acts 12:4, Herod Agrippa I assigned four quaternions — sixteen soldiers in total — to guard the imprisoned Peter: four soldiers on duty at a time, rotating through four watches of the night. Peter was chained between two soldiers while two more stood watch at the doors (Acts 12:6). This heavily reinforced guard, ordered by a king who had just executed James the brother of John, underscores the miraculous nature of Peter's deliverance by an angel — the escape was humanly impossible against such vigilance. The quaternion reflects standard Roman military guard procedure for high-value prisoners.