The official bodyguard of the Roman Emperor. It was founded by Augustus in 27 BC, and had a structure of 9 cohorts, 500 men each, under the command of the Praetorian Prefect. The guards served 16 year terms, and were generally experienced combat veterans. They received greater pay and privileges than the average soldier, and as the only permanent military force allowed in Rome, came to wield great power. Their power reached its height under the prefect Laetus, who organized the murder of the emperors Commodus and Pertinax (in 193 AD). They then sold the throne to Didius Julianus, who only ruled for 16 days before he killed Laetus, the Praetorians killed him, and Septimius Severus arrived with his legions and discharged every member of the Praetorian Guard. He then reorganized the guard, and it continued in its bodyguard function (without its former political clout) until it was dissolved by the emperor Constantine in 312.