How did police departments form
As societies became more urban and cities grew, maintaining security became a major priority for governments. Although threats in the ancient world and late antiquity were seen as external, it was also internal unrest that threatened cities and kingdoms. The development of policing was an important change that allowed cities to become safe enough to grow and prosper, but that history and its origin are complex.
In Mesopotamia and Egypt, but the 3rd millennium BCE, local officials appeared to have been tasked with rounding up criminals and bringing them to justice. The appearance of the first law codes during this time suggest crime was prevalent in cities and as urban places grew we begin to see an enforcement body, entrusted to local government officials, in charge with bringing in criminals and others who might have committed given crimes.
We learn more about the development of policing from ancient Greece. Although the term "police" derives from Greek origins, the concept of a civil force patrolling a city had not developed yet. Rather, the task of keeping relative calm and security in a city was something that was outsourced to slaves or servants who belonged to given officials. The Scythians were an ethnic group that came from Russia and Central Asia; some of these groups settled in Greece and warriors and slaves from these populations began to be used by city magistrates. The magistrates were responsible in using this force but most likely to also spy on the urban population to help maintain government control.
The city of ancient Rome probably had one of the most extensive policing forces, as the city's ancient size may have reached over a million inhabitants. Similar to Greece, magistrates used slaves to patrol and maintain order in Rome. Authority may have been problematic, as slaves were not seen as being able to give binding decisions such as arrested. Slaves, therefore, had to utilize the authority of their magistrates, and assume that their authority had credibility, in order to enforce their actions. However, by the period of Augusts in the late first century BCE and first century CE, the city of Rome developed the so-called vigiles, who acted as a group that were responsible for safety, security, and fire suppression (i.e, acted as a fire department). However, similar to earlier systems, these groups were privately owned slaves.
In ancient China, the development of the prefecture system by the mid-first millennium BCE, during the so-called Spring and Autumn period, included prefects given the responsibility with internal security in their regions. They became responsible in raising a force and enforcing an arrests of criminals. During the Tang dynasty, law enforcement became organized into a force called the Gold Bird Guards. This force was responsible in making arrests and was also assisted by citizens. The guards were composed of citizens.