Soldiers for military affairs and the Imperial Chancellor for central civilian administration. These reforms were the result of both the lack of officials suitable for the prefect's wide-ranging tasks, and of the desire to reduce the potential challenge to the Emperor's authority posed by a powerful Prefect. The next reforms were undertaken by Constantine I, who reorganised the supreme military command. Two significant parts of the reform are apparent: the separation of military commanders from civil administration and the division of the army into two classes: the Field Armies ("comitatenses") and the Frontier Troops ("limitanei"). The Field Armies served as the Empire's strategic reserve to respond to crisis where it may arise whereas the Frontier Troops were permanently stationed along the Empire's borders ("limes"). Recruited from the ranks of the Field Armies were the Palace Troops units ("Palatini"), who accompanied the Emperor as he travelled around the Empire, functioning as the successor to the Principate's Praetorian Guard. Around the same time, Constantine established the new military roles of the Master of the Soldiers ("Magister Militum"), who were the supreme military commanders of the empire. Beginning with the head of the foot troops, the magister peditum ("Master of the Foot"), and one for the more prestigious horse troops, the magister equitum ("Master of the Horse"), these were established in each of the four Praetorian Prefectures. Over time, the numbers and types of Masters would vary across the empire. The establishment of solely military officials provided for a more professional military leadership. The Masters were all ranked as illustres. Within the East, by the late 4th century, there were Masters of the Soldiers, per Illyricum, per Thracias , and per Orientem. Each of these three Masters exercised independent command over one of the three Field Armies of the Eastern Empire. There were also two Masters of the Soldiers in the Presence (in praesenti) who accompanied the Eastern Emperor and who each commanded half of the Palace Troops. Each of the five Masters were of equal rank. Within the West, there were originally four Masters of the Soldiers; foot and horse per Gallias and per Italiam. Over time, it became more common for the offices (foot and horse) to be combined under a single person, then styled magister equitum et peditum or magister utriusquae militiae ("master of both forces"). By the time of Stilicho, the Master of Both Services was the supreme military