A police force is any organized body of civilians directed by a government to maintain law enforcement and public order. While they often undergo combat training and are legally authorized to employ violence as necessary, they are distinct from the military in being a civil body entrusted only with domestic security.
Historically, the role of law enforcement was generally served by guards, soldiers which were garrisoned within a city for its defence. The existence of the police as a distinct body independent of the military is a relatively recent development. In ancient times, the responsibility of law enforcement was often bestowed upon specific arms of a military, such as the Medjay and Phylakitai of Egypt or the Jinyiwei of Ming dynasty China, a secret police which enforced the emperor's will against judicial rulings and purged dissenters under the pretense of preserving societal harmony.
The concept of the police as a professional, civilian organization did not develop until the late 18th to early 19th century. The United Kingdom did not have a unified force which specialized in the prevention and investigation of crime until they founded the Metropolitan Police Service in 1829, and this is sometimes taken as the first modern police force because it was decidedly intended to be civilian.  . By the time of the French Revolution, however, a force dedicated to criminal investigation had already been operating in Paris. Its development subsequently flourished under Eugène François Vidocq, a former criminal who pioneered the deductive method of detective work and founded the France's premier crime-fighting body, the Sûreté. Apart from this, the National Guard established by the French revolutionaries to protect themselves was also intended to be independent of the French Army. 
Police and the Assassins
The relationship between police and the Assassins can be complicated by the tendency of the latter to operate like vigilantes outside of the law in their quest to save humanity from the Templars. In one notable example, British police sergeant Frederick Abberline worked closely with Assassin twins Jacob and Evie Frye throughout 1868 in solving crimes and toppling the control of Templar Grand Master Crawford Starrick over London. However, the twins also founded a gang of their own, the Rooks, in their fight against Starrick's syndicate, the Blighters, and were by all means an extrajudicial party.
In later years, Abberline felt morally conflicted over his past partnership with the Assassins, but 2 decades later in 1888, he enlisted the aid of Evie Frye once again to stop the serial killer and rogue Assassin Jack the Ripper. Ultimately after Evie killed the Ripper, in spite of his misgivings, he agreed to her request to safeguard the mass murderer's fate and identity so as to protect the Assassins as a friend.
- Though Arno Dorian helps police chief Charles Cochon de Lapparent solve crimes in Assassin's Creed: Unity, police do not appear as a distinct gameplay faction until Assassin's Creed: Syndicate. There, they are color-coded blue on the mini-map. Although players are not penalized for killing them in free-roam, in various story memories, doing so costs full synchronization.
- The de-facto police in Assassin's Creed: Origins are referred to as phylakitai, both collectively and individually. This is incorrect as phylakitai is plural, with phylax being the singular equivalent. Even more confusingly, yet another version of the same word is used for the phylakes, again, both in plural and singular contexts, even though, again, the correct singular term is phylax.
- Assassin's Creed: Unity (first appearance)
- Assassin's Creed Chronicles: China (Mentioned only)
- Assassin's Creed: Syndicate
- Assassin's Creed: Origins
- ↑ Assassin's Creed
- ↑ Assassin's Creed II
- ↑ Assassin's Creed: Revelations
- ↑ Assassin's Creed III
- ↑ Assassin's Creed: Origins
- ↑ Assassin's Creed Chronicles: China
- ↑ Assassin's Creed: Syndicate – Database: Police
- ↑ Assassin's Creed: Unity – Murder Foretold
- ↑ Assassin's Creed: Unity – Database: Eugène François Vidocq
- ↑ Assassin's Creed: Syndicate
- ↑ Assassin's Creed: Syndicate – Jack the Ripper