The term derives from palatium ("palace") a reference to the fact that the regiments originally served in the imperial escort armies only.
There, however, they continued to enjoy higher status and pay than the rest of the comitatus regiments.
In the early 3rd century, the Roman military was organized into several provincial armies under the command of the provincial governors, a smaller reserve under the command of the emperor, guard units such as the Praetorian Guard, and the urban cohorts.
[3][4] In the later 3rd century, due to the frequent wars, field armies could remain together for several years, under the direct command of the emperor, and would require their own recruitment systems.
[4][5] By the mid 4th century, the Roman military was divided into frontier armies under the command of the provincial duces and permanent field armies under the command of the emperor, the magistri militum, magistri equitum, or comites.
[12] The temporary field armies could be referred to as the sacer comitatus,[13] as could the imperial court.
Parker, and more recently, Warren Treadgold and David S. Potter[19] attribute the reorganization to Diocletian.
[22][23] Karl Strobel sees the reorganization as the culmination of trends going back well into the 3rd century, with Diocletian strengthening both the frontier and field armies.
The late Roman empire had centralized fabricae, introduced by Diocletian, to provide arms and armor for the army.