Roman centurions were non-commissioned officers who commanded battle groups called "centuries," each comprising at least 100 men. Akin to sergeants in a modern army, centurions often led Rome's local police forces in occupied territories.
Centurions were responsible for keeping track of individuals who posed a threat to Rome's security. Because Jesus drew thousands of people to hear Him, He was perhaps kept under surveillance. That may account for the accurate knowledge that one officer seemed to have of Him (Luke 7:1-10>).