One Saturday in August 1286, the podestà of Bologna—the city's chief magistrate—dispatched some of his retainers to investigate a suspected gambling house not far from the piazza. They quietly surrounded the building, positioning four men at its rear escapes and three at its front door. From the doorstep they heard voices inside calling out bets, all but confirming their suspicion that the house was the site of illicit gaming. The podestà’s men ordered whomever was inside to open up at once. One of the alleged gamblers came to the front door but, seeing it was the podestà's men, alerted his companions in the back. Pandemonium erupted as the suspects scattered. Some fled through windows and over the rooftops of neighboring houses, while others hid under beds. But the podestà's men gave chase. Despite having to break down two doors to get inside, they managed to arrest nine fugitives before the dust settled. In the ensuing trial, the podestà's judge found all nine suspects and one other individual guilty of illicit gaming, and sentenced each to the statutory fine of 25 lire.

Conventional wisdom holds that police are an invention of modernity. In today's usage, “police” typically refers to the government entity responsible for civil order and law enforcement; “to police” is to perform the functions of a police department, namely to prevent and detect crime and bring criminals into custody. Social scientists and historians alike generally conceive of the police, along with the military, as the main instruments of the modern state’s claim to a monopoly on the legitimate use of violence within its territory. According to a popular Anglo-American narrative, modern policing did not exist until 1829, when Sir Robert Peel founded London's Metropolitan Police. As the story goes, the “bobbies” were a new kind of police, defined by their bureaucratic organization and preventive function. They were full-time, salaried public employees, unlike the part-time, parish-based watchmen who came before them. And their regular street patrols served to deter crime and maintain order, not merely detect crime and apprehend criminals after the fact.