Under the late Republic, a proconsul on campaign often formed a small personal guard, selected from the troops under his command, known as a "cohors praetoria" ("commander's cohort"), from "praetorium" meaning the commander's tent at the centre of a Roman marching-camp (or commander's residence in a legionary fortress). At the Battle of Actium (31 BC), Augustus had five such cohorts around him. After the battle, he retained them in being as a permanent brigade in and around Rome, known as the praetoriani ("soldiers of the imperial palace"). Inscription evidence suggests that Augustus increased the Praetorian establishment to nine cohorts, each under the command of a "tribunus militum" (military tribune). With all the legions deployed in far-off provinces under the command of powerful senators, Augustus evidently considered that he needed a least one legion-sized force with him in Rome to deter potential usurpers. Augustus stationed three cohorts in the City itself, each housed in separate barracks, and the rest in neighbouring cities of Latium. Originally, each cohort was independent, but in 2 BC, Augustus appointed two overall commanders ("praefecti praetorio") of equestrian rank, one for the cohorts based in the City, the other for those outside.