Legitimate emperors' reigns are shown in capitals. Usurpers and their reigns are shown in italics. The distinction between the two was often blurred. Many legitimate emperors, like Constantine, began their careers as usurpers.


Agentes in rebus: From the fourth century, the `agents in matters' were representatives of the emperor whose official task was to carry despatches. Since this involved travel and contact with many individuals, they also reported on the activities of other members of the imperial system. They were especially concerned to root out the disloyal. Their reports were one of the few ways that an emperor had of finding out what was going on in a distant province. Since their accusations so frequently led to the disgrace or death of officials and officers, they were as widely disliked as they were feared.

Arianism: This version of Christianity was declared heretical by the Council of Nicaea in 325. However, it continued to be widespread, especially in the eastern provinces throughout the fourth century. Its originator was Arius, a priest who taught at both Antioch and Alexandria. He asserted that Jesus was neither identical nor quite equal to God the Father. Precisely how this difference was defined varied amongst Arians. One of the commonest definitions was to say that God the Father and God the Son were `of like substance' (in Greek homoios). A version of Arianism remained common amongst groups like the Goths and Vandals into the sixth century.

Bucellarii: Soldiers paid and supported by a particular commander and forming part of his household. These men were still part of the regular army and supposed to be loyal to the emperor. The name derives from the ration hard-tack biscuit (bucellatum) and emphasised the commander's obligation to feed his soldiers. Such troops were common in the fifth and sixth centuries.

Candidati: Forty candidati were selected from the scholae regiments of the imperial bodyguard. They acted as personal bodyguards to the emperor. Their name was derived from their white uniforms. (Under the Republic, men standing for political office had also worn specially whitened togas, hence our word candidate.)

Cataphract: Heavily armoured cavalryman often riding an armoured horse. The Romans first encountered such warriors in eastern armies, but later made use of them themselves.

Clarissimus: Literally meaning `most distinguished', under the Principate the term was reserved for senators. By the fourth century it is instead associated with many imperial posts, both in the civil service and army.

Clibanarius: Heavily armoured cavalryman, whose horse may also have worn armour. It is unclear whether or not the term was synonymous with cataphract. The name came from a nickname meaning `bread-oven'.

Cohort (cohors): Under the Principate both legionaries and auxiliary infantry were divided into cohorts. This was the basic tactical unit of the army. Most cohorts were 480 strong, but the first cohort of a legion and some selected auxiliary units numbered Boo. By the fourth century only some units of limitanei were still organised into cohorts. These seem to have been much smaller than the earlier cohorts.

Cohortales: The staff and functionaries of provincial governors. From Constantine onwards this role was hereditary.

Colonus (pl. coloni): The coloni were tenant farmers. Diocletian tied such individuals to the land they worked in an effort to ensure regular tax revenue. Their descendants inherited the same obligations.

Comes (Count): Officers of the later Roman army, ranking below the Masters of Soldiers. A few of these officers were placed in charge of specific regions. Others were given command of parts of the comitatenses. Comes literally meant `companion' of the emperor and the title was also employed for a range of different posts.

Comes Domesticorum (Count of the Domestic Staff): From the middle of the fourth century this officer commanded the imperial bodyguard known as the protectores.

Comitatenses: The units of the `field armies' in the fourth, fifth and sixth centuries. In theory they were kept at the immediate disposal of the emperors or their commanders. They received better pay and privileges than the limitanei.

Consul: The year's two consuls were the senior elected magistrates of the Roman Republic and the year was named after them. The post of consul remained prestigious long after its real power had diminished. Emperors often held the consulship themselves. By the fifth century it was customary for the eastern and western emperors to appoint one consul each.

Cuneus: Title given to some cavalry units in the Late Roman army.

Curia: Town council composed of wealthier male members of the community. Its members were expected to spend considerable sums of their own money on local projects. In the Late Roman Empire it became difficult in many regions to find enough local men willing and able to serve on the councils.

Denarius: The basic silver coin under the Principate. It was the `penny' of the Authorised Bible, hence the pre-decimalisation abbreviation of d for pence. Denarii ceased to be minted in the third century, but many sums were still calculated in this unit.

Diocese: Having reduced the size of individual provinces, Diocletian created fourteen larger groupings known as dioceses for civilian administration. Each was the responsibility of a vicarius, who was himself junior to the praetorian prefects.

Dominate: Augustus and his successors had been known as princeps, or first citizen/magistrate. From Diocletian onwards, emperors preferred to be called dominus, which meant `lord' or `master'. Therefore, it is conventional for scholars to refer to the Late Roman Empire as the Dominate.

Donatists: This schismatic group took its name from its first leader Donatus. This split in the North African Church was not initially about questions of doctrine. Donatists objected to the readmission and continued service as priests or bishops of men who had fled or otherwise been discredited during the persecution of the Christians. Eventually, wholly parallel and distinct church organisations existed in many North African communities.

Dux (pl. duces): Senior officer in the Late Roman army, commanding a region and its garrison of limitanei.

Equestrian Order (Equites): The social class immediately below the senatorial order, the equiteswere named from their traditional role as the cavalrymen in the army of the Republic. Equestrians greatly increased their share of military and civil posts during the third century. Eventually, equestrian status was automatically bestowed by the holding of specific imperial posts, and the class itself was divided into several sub-groups of varying seniority.

Equites singulares Augusti: The emperor's own horse guards for the first three centuries of the Principate, these provided an elite cavalry force to support the praetorian guard. They seem to have been abolished when Constantine abolished the praetorian guard.

Foederati: Allied barbarians, obliged to provide military service to the emperor, who usually served in their own units and sometimes under their own commanders who usually held Roman rank.

Homoousios: This doctrine described Jesus as `of the same substance' as God the Father. It was adopted as the orthodox position by the bishops at the Council of Nicaea. In spite of some fierce resistance, it would eventually be confirmed as the doctrine of the orthodox Catholic Church.

Honoratus: retired imperial official, usually ranked as clarissimus. Such men enjoyed considerable prvileges.

Legatus: The senatorial representatives or deputies of the emperor. Under the Principate two types of imperial legates were most important: (i) The legatus Augusti pro praetore who held command in all imperial provinces (apart from Egypt) containing a legionary garrison; (2) The legatus legionis who commanded a legion.

Legion (Legio): Under the Principate the legion was a large formation of c.5,ooo men. Legions continued to exist in both the comitatenses and lirnitanei in the fourth and fifth centuries, but it is clear that they were much smaller in size. Legions of comitatenses are unlikely to have been much larger than i,ooo men and may well have been considerably smaller.

Limitanei: The grade of troops commanded by the duces limitis, the military commanders of the various regions, usually on the frontier, into which the provinces of the later empire were divided. They were paid less than the comitatenses.

Magister Officiorum (Master of Offices): The Magister Officiorum is first attested in the fourth century. The power of this rank gradually increased, until it became one of the most senior in the entire imperial bureaucracy and court. In addition to civil responsibilities, the Magister Officiorum controlled state arms factories and had some degree of control over the scholae.

Magistrates: The Roman Republic had employed elected magistrates as its senior executive officers. The most senior of these were the two consuls. Most of the posts continued to exist under the empire, but lost any political independence and were often appointments made by the emperors.

Manichaeism: This religion was founded by the prophet Mani in the third century. He had travelled widely, including a visit to India, and his ideas showed the influence of a wide range of different faiths, including Judaism, Christianity and Zoroastrianism. Mani spoke of a struggle between Light, or good, and Darkness, or evil. The world was a creation of Darkness that trapped elements of the Light within it. His most ardent followers lived rigorously ascetic lives in an effort to win redemption. Initially welcomed in Persia, he was eventually executed by King Bahram I in 276. Diocletian persecuted the followers of this religion, as did later Christian emperors.

Master of Soldiers (Magister Militum): These were the most senior military commanders below the emperors themselves from the fourth century onwards. There were several variations of this title. These included the Master of Horse (Magister Equitum) and Master of Infantry (Magister Peditum). In some cases the title also defined the region or sphere or responsibility. Not all Masters of Soldiers were of equal seniority, but the details of the rank structure varied over time.

Montanists: A Judaising Christian sect that appeared in the late second century and subsequently flourished, especially in Asia Minor. The Montanists initially were inspired by two women prophets who predicted the rapid approach of the Second Coming. The sect also emphasised the achievement of ritual purity through fasting, penances and retreat from ordinary life. The Montanist Church persisted with its own distinct hierarchy until the eighth century.

Neoplatonism: This descendant of Platonism developed in the third century from the teachings of the philosopher Plotinus, but incorporated ideas from other philosophical schools and fresh concepts. Neoplatonism became the dominant philosophical school of the Late Roman world. It included strong mystical elements.

Nicene Creed: See Homoousios.

Numerus (pl. numeri): Name given to units of irregular auxiliary soldiers under the Principate. Later the title was adopted by some cavalry units.

Palatini: Units of higher status and prestige than the comitatenses, the palatini also formed part of the field armies of Late Antiquity (4th-6th Century AD).

Patrician (Patricius): Although once an inner elite within the ranks of the Senate, in the fifth century this was used as a title by powerful generals, most notably Stilicho and Aetius.

Pilum (pl. pila): The heavy javelin that was the standard equipment of the Roman legionary for much of Rome's history, but seems to have fallen out of use during the third century.

Praepositus: Unit commander in the Late Roman army. It seems to have been virtually synonymous with tribune or prefect.

Praepositus sacri cubiculi: The senior eunuch official of the emperor's household. At times these men gained considerable influence. Theodoric, the Ostrogothic king of Italy, had one of these officials in his own court.

Praetorian Guard: The military bodyguard of the emperors of the Principate commanded by tribunes and the whole corps commanded by two praetorian prefects. Its position as the strongest armed body in Rome gave it considerable power. It was disbanded by Constantine in 312 after supporting his rival Maxentius.

Praetorian Prefect: Originally the commanders of the praetorian guard, as the third century developed the praetorian prefects developed into something more like senior bureaucrats or grand viziers. By the fourth century they had lost all real military responsibilities and did not command troops. Their number also increased and the post tended to oversee a specific region of the empire. The vicars were their subordinates.

Primicerius notariorum (Head of the Notaries): The senior notary had particular charge of issuing appointments and commissions. The Notitia Dignitatum was originally prepared by his department.

Primicerius sacri cubiculi: This was the second most senior eunuch of the imperial chamber. Once again, close access to the emperor himself often meant that these acquired considerable influence.

Principate: Augustus claimed to be merely the princeps, the most senior magistrate/citizen in the state. Therefore the regime he created is conventionally referred to as the Principate. It lasted from the late first century BC until its collapse during the third century.

Protectores domestici: This was the close imperial bodyguard. It seems to have existed from at least the time of Diocletian. In some respects it served as an officer cadet unit, since its members were frequently given command of units in the wider army.

Rescript: Formal reply issued by an emperor in response to a petition. These rulings were legally binding.

Schola: Guard cavalry regiment in the later Roman army. In the Notitia Dignitatum five scholae are listed for the Western Empire and seven for the Eastern Empire.

Senate: This body of some boo members that met in Rome enjoyed considerable prestige even after it had ceased to wield real political power. Later, Constantinople acquired a Senate of its own.

Senatorial Order: In the Principate membership of the senatorial order required the possession of considerable property, including at least some land in Italy. The status was kept for two generations after an individual had actually been a member of the Senate. Later, senatorial status came as a result of holding high imperial office.

Solidus: This gold coin was introduced in the fourth century, in part because the taxation system and other imperial finances needed to be based on more stable gold values. There were seventy-two coins to a pound of gold.

Spatha: The name conventionally used to describe the longer swords used by Roman cavalrymen and, in Late Antiquity, also many infantrymen.

Stoicism: One of the main philosophical schools popular in the Principate, stoicism was founded by the philosopher Zeno in the late fourth century BC. Marcus Aurelius was one of its most prominent adherents.

Tetrarchy: The Rule of Four Emperors was introduced by Diocletian. There were two senior colleagues, each with a title of Augustus, and each of these had a junior assistant, who was titled Caesar. Pronouncements and laws were all issued in the four names. The system did not last in this form.

Trecenarius: Junior officer in the Late Roman army.

Vicar (Vicarius): The vicar was the civil administrator in charge of a diocese.

Zoroastrianism: The religion of ancient Persia, which may well have originated around 1000 BC. It was revived and became far more prominent with the establishment of the Sassanid dynasty by Ardashir in the third century. Its worship was marked by specially designed temples, which housed the sacred fire.

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