II. Ancient and Classical Periods, 3500 B.C.E.–500 C.E. > E. Rome > 5. The Later Empire, 284–527 C.E. > b. Diocletian and the House of Constantine
  The Encyclopedia of World History.  2001.
b. Diocletian and the House of Constantine
The advent of Diocletian saw a thoroughgoing administrative reform of the Empire. Since it is difficult to distinguish which innovations were due to Diocletian and which to Constantine, a general summary will be given here. Senatorial governors of provinces had been first relegated to solely civic functions, then virtually eliminated in favor of equestrians by Diocletian. At Rome, the power of the senate and of magistrates waned when the emperor and his court moved to cities closer to the theaters of war. The function of the Roman senate was limited to governing the city of Rome. Meetings, presided over by the urban prefect, were often unattended, most senators preferring to remain on their estates. But the prestige of the Roman senate was sufficiently high in the 4th century for Constantine to established a second senate at his new capital of Constantinople. Over the course of the 3rd century, the duties of most traditional Roman magistracies had been either eliminated or absorbed by equestrian officials appointed by the emperor. The consulship survived as a largely honorary office. In the 3rd century its prestige declined, but it was revived in the 4th, when Constantine established two annual consuls in Constantinople to match the pair in Rome. Thereafter, in the west the consulship became the prerogative of a narrow circle of aristocratic Roman families, while in the east the office tended to be monopolized by emperors, or used by them to reward both military and civic service. The emperor was chosen by the army and ruled absolutely. Beginning with Diocletian, the pomp and ceremony of the Persian court was adopted. The emperor was lord (dominus), and everything surrounding him sacred (sacrum). He wore a diadem, purple and gold robes, and jeweled slippers. Subjects prostrated themselves in his presence. The imperial court (comitatus) comprised great numbers of officials which included a large domestic staff headed by a eunuch, various offices (officia), and a magister memoriae (master of records), all supervised to one degree or another by the magister officiorum. In addition, there was the imperial guard (scholae), from which 40 men were selected to be the emperor's bodyguard (called candidati after their white uniforms). Also present at court was the officer training corps (protectores), in which promising officers served for a few years before being posted to high office. At court, protocol ruled.  1
The Empire was divided for administrative purposes into two spheres, eastern and western. Instituted by Diocletian, the division was in effect sporadically during the 4th century and became permanent with Arcadius and Honorius (395). Under Diocletian's tetrarchic system, there were two co-ruling senior emperors (Augusti), one in the east, the other in the west. Each Augustus chose an assistant and successor (Caesar). Imperial edicts were issued in the names of all four. There were four praetorian prefects who served under each of the four rulers and administered the four prefectures—Gaul, Italy, Illyricum, and the east. Each prefecture was divided into several dioceses under vicarii (vicars). In 312 Constantine disbanded the praetorian guard; and the prefects, together with their subordinate vicars, lost all military functions which were transferred to a magister militum. The dioceses were subdivided into provinces, which had themselves been divided so that their number doubled. Provinces were under the supervision of equestrian governors called praesides. Italy assumed the status of a province, its districts supervised by senatorial correctores.  2
In the late Empire, the military was wholly separated from the civilian administration, with the army bureaucracy usurping many administrative functions. The imperial armies of the high Empire had been tied to the defense of particular provinces. The system had proved inadequate during the third-century invasions, and so two distinct types of armies had developed. In the provinces, stationed along the borders, were the frontier armies made up of resident soldiers (limitanei) and commanded by a dux. A larger, better trained, and more mobile field army (comitatenses) was under the command of masters of infantry and cavalry (magistri peditum, equitum). Auxiliary troops were mostly foreign soldiers commanded by their own leaders, some of whom became very influential. Under Constantine a large part of the field army stayed with the emperor. Another contingent was permanently stationed on the eastern frontier under a magister equitum et peditum per Orientem, while the west was defended by another field army stationed in Gaul and commanded by a magister equitum et peditum per Galliam. Smaller units of the field army, stationed in Illyricum and Thrace, were commanded by officers called comites rei militaris. The size of all these units is controversial. Diocletian seems to have increased the numbers of legions of the frontier army from about 40 to 60. Under Constantine the field army might have reached 200,000 men. The Roman armies of the 4th century have been estimated at between 500,000 and 730,000 men.  3
Diocletian attempted to create a more efficient tax system. He established a regular system of requisitioning food and transport, and his taxes were based both on the iugum (a unit of land) and the caput (a unit of labor) and included Italy. Annual estimates were made for the imperial costs for the army, administration, and city of Rome, and a budget was produced to which taxes were adjusted. To facilitate the reform, a new census was conducted. Diocletian's attempt to control inflation by fixing prices and maximum wages in his Edict on Prices (301) resulted in goods being withdrawn from market and in violence, while prices continued to rise.  4
Gaius Aurelius Valerius DIOCLETIANUS (Diocletian, b. 245, saluted as emperor Nov. 284).  5
Upon the defeat of Carinus, Diocletian chose as his colleague the Illyrian, M. Aurelius Valerius Maximianus (Maximian), who was given the title of Caesar.  6
After suppressing the peasant revolt of the Baucaudae in Gaul, Maximian was raised to the position of Augustus. Diocletian took up residence at Nicomedia in Bithynia, while Maximian lived mostly at Mediolanum (Milan). Diocletian assumed the title Jovius, and Maximian assumed that of Herculius.  7
Diocletian and Maximian waged constant war to hold the Empire together. Maximian was unable to oust M. Aurelius Mausaeus Carasius, who had seized the province of Britain and declared himself Augustus.  8
293, Mar 1
Creation of the Tetrarchy. Diocletian chose as his subordinate Caesar, C. Galerius Valerius Maximianus (b. c. 250). Galerius became Diocletian's son-in-law and governed most of the Balkan provinces; Diocletian governed the rest of the east. Maximian chose as his Caesar, Flavius Valerius Constantius, who divorced his wife Helena to marry Maximian's daughter. Constantius governed Gaul whence he drove Carasius to Britain, where he was killed and superseded by Allectus.  9
Constantius crossed to Britain, defeated and killed Allectus, and restored Britain to the Empire. Egypt revolted under Aurelius Achilleus, and L. Domitius Domitianus was proclaimed emperor. Diocletian put down the revolt in the winter of 296–7.  10
Narseh (Narses), the king of Persia, expelled the pro-Roman king of Armenia (See 297). Galerius invaded Persia and was defeated but returned in the following year to crush the Persians. Narseh ceded Mesopotamia and other territories east of the Tigris to Rome.  11
Constantius returned to Gaul and defeated the Alamanni.  12
Diocletian's Edict on Prices.  13
303, Feb. 23
Galerius persuaded Diocletian to declare a general persecution of the Christians, which, however, Constantius did not fully enforce in his prefecture. The persecution was stopped in the entire west in 306 but raged in the east until 313.  14
305, May 1
Diocletian and Maximian abdicated voluntarily; Galerius and Constantius became Augusti; Diocletian and Galerius selected as Caesars Flavius Valerius Severus under Constantius, receiving the prefecture of Italy, and for Galerius his own nephew Galerius Valerius Maximinus Daia, who received Syria and Egypt. The hereditary claims of Maximian's son Maxentius and Constantius's son Constantine were neglected.  15
The Encyclopedia of World History, Sixth edition. Peter N. Stearns, general editor. Copyright © 2001 by Houghton Mifflin Company. Maps by Mary Reilly, copyright 2001 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.