Vigiles (Vigiles Urbani or Militia Vigilum) were established in the 6 CE by Augustus. It was a paramilitary formation consisting of seven cohorts probably counting 1000 people each (I-VII). The task of the vigils was to perform the role of the police and on the other hand the fire brigade. Each cohort was assigned to two of the fourteen districts of Rome. Cohorts had a permanent base (castra) and guard points (excubitoria) in the city.
This corps was considered a part of the permanent army, and the officers serving in it were promoted to the Roman legions. Modern Italian fire brigade is considered to be a continuator of this tradition, hence its name Vigili del Fuoco.
At the head of cohortes vigilum was prefect (praefectus vigilum). Since the time of Trajan, the office of the deputy prefect (subpraefectus vigilum) has appeared. Each cohort was divided into seven centurions commanded by centurions. In addition to Rome, additional cohort of Vigiles stationed in Puteoli and Ostia. The service in this formation was performed by the freedmen, who, since the ruling of Tiberius, were guaranteed the receive Roman citizenship after six years of service. Then the period was reduced to even three years. In the formation was able to serve – from the 2nd century CE – also Roman born citizens.
The whole unit was located in seven barracks in Rome, divided into 14 districts. In each district there was also a post (excubitorium), in which vigiles were serving. It should be assumed that each cohort was staffed with two posts.
Similar units were created later, also in several other cities of the Roman Empire, including in Ravenna, Nemausus (Nimes) and Lugdunum (Lyon).