The Cohortes Praetoriae are the core of the emperors' guard in Roma and considered as the best infantry in the empire.

New Praetorians can only be trained in their garrisons in Latium, the Empire’s heart, where they protect Roma, the seat of the imperial government.

The Cohortes Praetoriae are the highest ranked units in the whole imperial army. Their infantry is the core of the Emperor's Guard in Roma and is considered the best in the empire. Praetorians are equipped as, and fight in, the same manner as the normal legionnaires, but their look is often somewhat more magnificent. Their lack of experience in actual combat is compensated by excellent, continuous training, and capable officers. High quality equipment has become one of the great strengths of the Roman heavy infantry, besides their strict discipline. The soldiers of the cohortes praetoriae wear coats of lorica hamata, greaves on both legs, imperial Gallic iron helmets and half oval scuta for protection. Their weapons, the same as in contemporary legions, are a type mainz gladius, two pila and a short dagger called the pugio.

Historically, generals in the late republic began to form cohorts of elite legionnaires for their own protection, and as an elite tactical reserve. They were called praetorians for guarding the "Praetorium", the tent or house of a Roman Army’s commanding officer. After the civil war Augustus reformed his praetorians into a permanent guard with nine cohorts of 500 infantry and 90 cavalry. Each of them was organized independently and commanded by an equestrian tribune. Three were stationed in Roma, the others in surrounding towns in Latium and Umbria.

In the early Principate, Praetorians were mostly recruited in central Italy and had to serve 16 years under excellent conditions and better pay compared to the frontier legions. After their discharge they received a high cash bonus, the praemia militare, or a small piece of land. Later, during Augustus' reign, the praetorian guard was commanded by two, and finally one praefect of equestrian rank, soon one of the most powerful men in the empire. In 23 AD, Tiberius, influenced by his praetorian prefect Seianus, concentrated all cohorts in a single fort in Roma on the Viminal hill.