 In the long history of the Roman Empire, the character of the military policy of the Roman Empire changed, and consequently the location and dimension of the castra changed.Under Emperors Gallienus and Aurelian (and later Diocletian), the Roman army was organized into a high-mobility central army (the "comitatus") and in local troops (the "limitanei").Some castra lost importance, others were built in new zones, and in general they lost the role of permanent quarter for huge corps of troops.