This chapter discusses how, during the period known as the Dark Ages and then the Middle Ages, a few policing institutions began to be developed, but often their existence could be brief and limited in scope. Throughout the period, princes had to fight to gain or maintain territory, and ensuring the safety of frontiers meant that they appointed administrators and/or warriors to protect territory, or to bring in soldiers and revenue as and when necessary. The warriors, increasingly known as knights, established themselves as hereditary rulers over the territory granted to them by the prince. Municipalities could acquire a significant degree of independence from the local prince, and they were permitted to establish their own laws; they also recruited men to enforce those laws, which included market regulation, the supervision of abattoirs, watching for fire, and ensuring the safety and tidiness of the streets. The municipal guards, often backed by all fit men in a town, might also be called upon occasionally to defend the walls and outlying territory. The chapter then considers the role of warrior monks, clergy, and feudal municipalities. Ultimately, officers such as bailiffs, sheriffs, or constables, and institutions such as the watch, emerged across medieval Europe, but they were not police officers in the sense of people seeking to prevent crime or regularly gathering information about offences and pursuing offenders beyond their boundaries.