By the turn of the millennium, Emperor Augustus' primary military concern was to prevent Roman generals from further usurping the imperial throne. The experience of Caesar and, earlier, Marius and Sulla, had demonstrated the willingness of "emergency" (re-activated previously decommissioned) legions containing troops keen for plunder to follow their generals against the state. Augustus therefore removed the need for such emergency armies by increasing the size of the standing armies to a size sufficient to provide territorial defence on their own.* Smith, "Service in the Post-Marian Roman Army", p. 71</ref> Perhaps due to similar concerns, the legions and auxiliaries of the army were supplemented under the Emperor Augustus by an elite formation of guards dedicated to the protection of the Emperor. The first such unit was based in Rome and were known as the Praetorian Guard, and a second similar formation were known as the Cohortes urbanae.