Police are the enforcers of law in a society. Their job entails investigating crimes and arresting suspected criminals to be brought to trial. They also act as witnesses to crimes and are often called upon to give evidence against an accused. Police are required in every civilized society, as they are necessary to enforce the Rule of Law. Police are also known as constables, inspectors, sheriffs, and troopers. Each has a specific function as deemed by their respective governing agency.
The history of the police as a job function dates back beyond the Roman and Greek eras. Prior to this, the function of law and order was left to the particular nobles to protect their own lands. During the Roman Empire, law and order was more organized, as the military performed this function. In ancient Rome, the Praetorian Guard acted as the police force.
In the United Kingdom, the modern police force as it is known today was originally established by the prime minister Robert Peel in the nineteenth century. To this day, policemen are colloquially known as "bobbies" or (less frequently) "peelers" in recognition of Peel's role.