The urban cohorts (cohortes urbanae) were a police-military formation initially composed of three cohorts. The service in this formation could be performed by persons with Roman citizenship. The analysis of the inscription material showed that over 80% of the soldiers of this formation came from Italy alone. The rest came from the provinces.
The city cohorts, created during the reign of Octavian Augustus, were initially under the authority of the prefects of the Praetorian Guard and then came under the direct control of the Prefect of Rome (praefectus Urbi). The relationship between cohortes urbanae and the Praetorian Guard was confirmed by designating the cohorts of this formation with numbers from X to XII, which constituted the continuity of the numbering of the praetorian cohorts (from I to IX). Both of these units were also quartered together in the cohortes praetoriae (castra praetoria) barracks practically until 270 CE when the city cohorts received their own camp in the Field of Mars (castra urbana). In addition to Rome, single cohortes urbanae were stationed in Puteoli, Osti, Carthage and Lyon. From the second half of the 1st century CE, four city cohorts were stationed in Rome. One cohort was placed in Carthage and Lyon (cohors and Flavia Urbana). Each cohort, led by a tribune, was made up of six centuries.
The size of the city cohorts was 480 – 500 people. In the sixties of the first century CE, this number was briefly increased to 1,000, and then halved again under the Flavian rule. City cohorts began to count 1,500 people since the reforms of Septimius Severus carried out in the 1990s of the 2nd century CE. Cohortes urbnae consisted of pedestrian cohorts, with the exception of cohors urbana stationed in Carthage, where there were also riders in the state. The duration of the service was 20 years. This formation avoided the fate of the Praetorian Guard and functioned in the 4th century CE. losing its military character over time.