Gallienus in the context of Antoninianus

Early Christians were heavily persecuted throughout the Roman Empire until the 3rd century. Although Christianity initially emerged as a small Jewish movement in 1st-century Judaea, it quickly branched off as a separate religion and began spreading across the various Roman territories at a pace that put it at odds with the well-established Roman imperial cult, to which it stood in opposition; Christians were vocal in their expressions of abhorrence towards the beliefs and practices of Roman paganism, such as deifying and making ritual sacrifices to the Roman emperor or partaking in other methods of idolatry. Consequently, the Roman state and other members of civic society routinely punished Christians for treason, various rumoured crimes, illegal assembly, and for introducing an alien cult that drove many Roman people to apostasy in favour of Jesus Christ. According to Tacitus, the first wave of organized persecution occurred under Nero (r. 54–68), who blamed Christians for the Great Fire of Rome in 64. A number of mostly localized persecutions occurred during the reign of Marcus Aurelius (r. 161–180). After a lull, persecution resumed under Decius (r. 249–251) and Trebonianus Gallus (r. 251–253). The Decian persecution was particularly extensive, as Decius strived to restore the Roman golden age in part by forcing pagan practices upon the Christian community. Another wave of persecution began under Valerian (r. 253–260), but ceased abruptly after he was captured and taken prisoner by the Sasanian Empire during the Battle of Edessa of the Roman–Persian Wars. Under his successor Gallienus (r. 253–268), whose reign was marred by rapidly escalating military conflicts of the Crisis of the Third Century, the first ever decree of tolerance was issued for Christian practices and places of worship, although it stopped short of recognizing Christianity as a religion with legal status.

Emperor Diocletian (r. 283–305) began the Diocletianic persecution, which was the final and the most severe wave of persecution of Christians by the Roman state. It was enforced until the accession of Galerius (r. 305–311), who issued the Edict of Serdica, and the death of Maximinus Daza (r. 310–313). After Constantine the Great (r. 306–337) defeated his rival Maxentius (r. 306–312) at the Battle of the Milvian Bridge in October 312, he and his co-emperor Licinius issued the Edict of Milan, which decriminalized Christianity and suppressed pagan populations throughout the Roman Empire. In 380, Theodosius I (r. 379–395) issued the Edict of Thessalonica, officially establishing Christianity as the Roman state religion. It was also during the reign of Theodosius I that pagan practices were overtly deemed punishable offenses, which laid the framework for early Byzantine anti-pagan policies.

The Illyrian emperors (Latin: Illyriciani) were a group of Roman emperors during the Crisis of the Third Century who were of Illyrian origin and hailed from the region of Illyria (Latin: Illyricum, in the Western Balkans), and were raised chiefly from the ranks of the Roman army (whence they are ranked among the so-called "barracks emperors"). In the empire the Illyrian generals had established a powerful military caste.

In the 2nd and 3rd centuries, the Illyricum, which included the provinces on the Lower Danube (Dacia, Raetia, Pannonia, Moesia), held the largest concentration of Roman forces (12 legions, up to a third of the total army), and were a major recruiting ground. The advance of these low-born provincials was facilitated by a major shift in imperial policy from the time of Gallienus (253–268) on, when higher military appointments ceased to be exclusively filled by senators. Instead, professional soldiers of humble origin who had risen through the ranks to the post of primus pilus (which also entailed admission to the equestrian order) were placed as heads of the legions and filled the army's command structure.

Aurelian (/ɔːˈriːliən/; Latin: Lucius Domitius Aurelianus; 9 September c. 214 – c. November 275) was a Roman emperor who reigned from 270 to 275 during the Crisis of the Third Century. As emperor, he won an unprecedented series of military victories which reunited the Roman Empire after it had nearly disintegrated under the pressure of barbarian invasions and internal revolts. For his success in restoring the Empire's territorial integrity, Aurelian was honored with the title Restitutor Orbis ("Restorer of the World"). Born in modest circumstances, most likely in Moesia Superior, he entered the Roman army in 235 and climbed up the ranks. He went on to lead the cavalry of the emperor Gallienus, until Gallienus' assassination in 268. Following that, Claudius Gothicus became emperor until his own death in 270. Claudius' brother Quintillus then ruled for three months, before Aurelian took the empire for himself. Aurelian was chosen Roman emperor by the Illyriciani as one of themselves.During his reign, he defeated the Alamanni after a devastating war. He also defeated the Goths, Vandals, Juthungi, Sarmatians, and Carpi. Aurelian restored the Empire's eastern provinces after his conquest of the Palmyrene Empire in 273. The following year he conquered the Gallic Empire in the west, reuniting the Empire in its entirety. He was also responsible for the construction of the Aurelian Walls in Rome, the abandonment of the province of Dacia, and monetary reforms attempting to curb the devaluation of the Roman currency.Although Domitian, two centuries earlier, was the first emperor who had demanded to be officially hailed as dominus et deus ('master and god'), these titles never occurred in written form on official documents until the reign of Aurelian. His successes were instrumental in ending the crisis.

Valerian (/vəˈlɪəriən/ və-LEER-ee-ən; Latin: Publius Licinius Valerianus; c. 199 – 260 or 264) was Roman emperor from 253 to spring 260 AD. He rose to power during a particularly unstable period during the Crisis of the Third Century and appointed his son Gallienus as co-emperor.

Valerian is known as the first Roman emperor to have been taken captive in battle, captured by the Persian emperor Shapur I after the Battle of Edessa, causing shock and instability throughout the Roman Empire. The unprecedented event and rumors of his humiliation at the hands of the Persian emperor generated a variety of different reactions and "new narratives about the Roman Empire in diverse contexts".

The Usipetes or Usipii (in Plutarch's Greek, Ousipai, and possibly the same as the Ouispoi of Ptolemy) were an ancient Germanic people who entered the written record when they encountered Julius Caesar in 56/55 BC when they attempted to find a new settlement west of the Rhine, together with the Tencteri, who were both attempting to move away from the aggressions of the Suevi on the east side of the Rhine. After the Romans slaughtered a great number of both tribes, they resettled on the east bank with the help of the Sicambri.

By about 100 AD, in the time of the Roman author Tacitus, the Usipii and Tencterii had moved southwards along the eastern bank of the Rhine into a position between the Chatti and the river. During the reign of Gallienus around 260-268 AD, the Laterculus Veronensis, reports that the Romans lost control of the Usipii lands, and after this they no longer appear in historical records.

The Diocletianic or Great Persecution was the last and most severe persecution of Christians in the Roman Empire. In 303, the emperors Diocletian, Maximian, Galerius, and Constantius issued a series of edicts rescinding Christians' legal rights and demanding that they comply with traditional religious practices. Later edicts targeted the clergy and demanded universal sacrifice, ordering all inhabitants to sacrifice to the Roman gods (Jews were exempt). The persecution varied in intensity across the empire—weakest in Gaul and Britain, where only the first edict was applied, and strongest in the Eastern provinces. Persecutory laws were nullified by different emperors (Galerius with the Edict of Serdica in 311) at different times, but Constantine and Licinius' Edict of Milan in 313 has traditionally marked the end of the persecution.

Christians had been subject to intermittent local discrimination in the empire, but emperors prior to Diocletian were reluctant to issue general laws against the religious group. In the 250s, under the reigns of Decius and Valerian, Roman subjects including Christians were compelled to sacrifice to Roman gods or face imprisonment and execution, but there is no evidence that these edicts were specifically intended to attack Christianity. After Gallienus's accession in 260, these laws went into abeyance. Diocletian's assumption of power in 284 did not mark an immediate reversal of imperial inattention to Christianity, but it did herald a gradual shift in official attitudes toward religious minorities. In the first fifteen years of his rule, Diocletian purged the army of Christians, condemned Manicheans to death, and surrounded himself with public opponents of Christianity. Diocletian's preference for activist government, combined with his self-image as a restorer of past Roman glory, foreboded the most pervasive persecution in Roman history. In the winter of 302, Galerius urged Diocletian to begin a general persecution of the Christians. Diocletian was wary and asked the oracle at Didyma for guidance. The oracle's reply was read as an endorsement of Galerius's position, and a general persecution was called on 23 February 303.

The Battle of Naissus in 268 or 269 was the defeat of a Gothic coalition by the Roman Empire under Emperor Gallienus (or Emperor Claudius II Gothicus) and the future Emperor Aurelian near Naissus (Niš). The events around the invasion and the battle are an important part of the history of the Crisis of the Third Century.

The result was a great Roman victory which, combined with the effective pursuit of the invaders in the aftermath of the battle and the energetic efforts of the future Emperor Aurelian, largely removed the threat from Germanic tribes in the Balkan frontier for the following decades.

This is a list of Roman army units and bureaucrats.

• Accensus – Light infantry men in the armies of the early Roman Republic, made up of the poorest men of the army.
• Actuarius – A soldier charged with distributing pay and provisions.
• Adiutor – A camp or headquarters adjutant or assistant.
• Aeneator – Military musician such as a bugler
• Agrimensor – A surveyor (a type of immunes).
• Antesignano – Supposedly a light infantry unit of legionaries who were used for protection of marching columns and to provide security to legions.
• Aquilifer – Bearer of the legionary eagle.
• Ala – a military formation composed of conscripts from the Italian military allies.
• Alaris – A cavalryman serving in an ala.
• Auxilia – were introduced as non-citizen troops attached to the citizen legions by Augustus after his reorganisation of the Imperial Roman army from 30 BC.
• Architecti – An engineer or artillery constructor.
• Armicustos – A soldier tasked with the administration and supply of weapons and equipment. A quartermaster.
• Ballistarius – An artillery operator (a type of immunes).
• Beneficiarius – A soldier performing an extraordinary task such as military policing or a special assignment.
• Bucellarii – were formations of escort troops.
• Bucinator – A trumpeter or bugler.
• Cacula – Servant or slave of a soldier.
• Capsarior – A medical orderly.
• Causarius – A soldier discharged for wounds or other medical reasons.
• Celeres - A royal guard created by Romulus to guard the King of Rome.
• Centurion – Officer rank, generally one per 80 soldiers, in charge of a centuria.
• Clinicus – A medic.
• Cohors amicorum – Military staff company functioning as suite and bodyguard of a high Roman official.
• Comes – commanders of comitatenses. The authority of a comes was limited to his assigned territory. This title later evolved to the medieval title of Count.
• Comes stabuli – An office responsible for the horses and pack animals.
• Comitatenses – units of the field armies of the late empire. They were the soldiers that replaced the legionaries.
• Cornicen – A bugler.
• Doctor – A trainer, subdivisions for everything from weapons to horn blowing.
• Draconarius – Bearer of a cavalry standard.
• Decurion – Leader of a troop of cavalry (14-30 men). Not to be confused with decanus.
• Decanus – Leader of a contubernium (a legionary tent group of 8 men). Elected by the members of the contubernium.
• Discens – Miles (enlisted soldier) in training for an immunis position.
• Duplarius – A soldier issued double pay, such as an Optio or a minor cavalry officer as part of a Turma
• Dux – A general in charge of two or more legions. In the Third Century AD, an officer with a regional command transcending provincial boundaries, responsible directly to the emperor alone, usually appointed on a temporary basis in a grave emergency. In the fourth century AD, an officer in charge of a section of the frontier answering to the Magister Militum. Later developed into the medieval title Duke.
• Duumviri navales – Two men elected to equip and repair the Roman navy.
• Equites singulares Augusti – Elite cavalry unit tasked to guard the Roman Emperors. Usually commanded by a tribunus of praetorian rank.
• Evocatus – "One who is called back." A soldier who had served out his time and obtained his discharge (missio), but had voluntarily enlisted again at the invitation of the consul or other commander.
• Evocatus Augusti – Praetorian Guard who had served out his time and obtained his discharge (missio), but had voluntarily enlisted again.
• Equites – Roman cavalry. Those citizens whose personal wealth was sufficient to own and equip a horse for cavalry, later evolved into a socioeconomic distinction unrelated to military service.
• Foederati – For groups of "barbarian" mercenaries of various sizes who were typically allowed to settle within the empire after service in the imperial army. Foederati, unlike auxilia which were commanded by Roman officers, and enlisted under the promise of obtaining Roman citizenship after completing their term of service of 20 to 25 years, were enlisted as an entire tribal unit, serving under native commanders, and not eligible to receive citizenship. Originally paid in money, but as the finances of the Late Empire declined, service in exchange for land became the norm. The sack of Rome in the 5th century by Vandals and Ostrogoths were precipitated by the Senate's failure to pay foederati as promised after their military service. The system of land tenure established by the settlement of foederati, whose leaders were granted territories as their personal property, developed into the medieval system of feudalism.
• Frumentarii – Officials of the Roman Empire during the 2nd and 3rd era. Often used as a Secret Service, mostly operating in uniform.
• Hastatus – The youngest of the heavy infantry in the pre-Marian armies, who were less well-equipped than the older Principes and Triarii. These formed the first line of battle in front of the Principes.
• Hastatus Prior – A centurion commanding a manipulus or centuria of hastati. A high-ranking officer within a manipulus or centuria.
• Hastatus Posterior – A deputy to the hastatus prior
• Hastiliarius – A weapons instructor.
• Imaginifer – A standard-bearer carrying the imago – the standard which bore a likeness of the emperor, and, at later dates, his family.
• Immunes – Soldiers who were "immune" from combat duty and fatigues through having a more specialist role within the army.
• Jovians and Herculians – A senior palatine units
• Katepano – A Byzantine military rank or military official.
• Laeti – was a term used in the late empire to denote communities of foreigners permitted to settle on, and granted land in, imperial territory on condition that they provide recruits for the Roman military.
• Legatus legionis – A legion commander of senatorial rank; literally the "deputy" of the emperor, who was the titular commander-in-chief.
• Limitanei – A unit of frontier districts.
• Legatus pro praetore – Provincial governor of senatorial rank with multiple legions under his command.
• Legionary – The heavy infantry that was the basic military force of the ancient Roman army in the period of the late Roman Republic and the early Roman Empire.
• Magister militum - High ranked commander in the late Roman Empire. Equivalent of a general.
• Medicus – Physician or combat medic. Specializations included surgery (medicus vulnerarius), ophthalmology (medicus ocularius), and also veterinary (medicus veterinarius). At least some held rank equivalent to a centurion.
• Megas doux – Commander-in-chief of the Byzantine navy.
• Miles or Miles Gregarius – The basic private level foot soldier.
• Numerus – A unit of foreign allies not integrated into the regular army structure. Later, a unit of border forces.
• Numerus Batavorum – was a personal, imperial guards unit for the Roman emperors of the Julio-Claudian dynasty (30 BC – AD 68) composed of Germanic soldiers.
• Optio – One per century as second-in-command to the centurion. Could also fill several other specialized roles on an ad hoc basis.
• Palatini – were elite units of the late army.
• Pedites – The infantry of the early army of the Roman kingdom. The majority of the army in this period.
• Peditatus – A term referring to any infantryman in the Roman Empire.
• Pilus Prior – Senior centurion of a cohort.
• Pilus Posterior – Deputy to the pilus prior.
• Praefectus Castrorum – Camp prefect, third-in-command of the legion, also responsible for maintaining the camp, equipment, and supplies. Usually a former primus pilus.
• Praefectus Cohortis - Commander of a cohort.
• Praefectus legionis agens vice legati – Equestrian officer given the command of a legion in the absence of a senatorial legatus. After the removal of senators from military command, the title of a legionary commander. ("...agens vice legati, dropped in later Third Century")
• Praetorians – A special force of bodyguards used by Roman Emperors.
• Praetorian prefect – Commander of the Praetorians.
• Primani – was a legio palatina, active in the 4th and 5th century.
• Primicerius – was a rank junior to the tribunus and senior to the senator.
• Primus Ordinis – The commanding officer of each centuria in the first cohort with the exception of the first centuria of the cohort.
• Primus Pilus (literally 'first file' ) – The centurion commanding the first cohort and the senior centurion of the entire Legion.
• Princeps – Pre-Marian soldier, initially equipped with the Hasta spear, but later with the pilum, these men formed the second line of battle behind the Hastati in the pre-Marian armies. They were also chieftains in Briton like Dumnorix of the Regneses (he was killed by Gaius Salvius Liberalis' soldiers).
• Princeps Prior – A centurion commanding a century of principes.
• Princeps Posterior – A deputy to the princeps prior.
• Principales – A group of ranks, including aquilifer, signifer, optio, and tesserarius. Similar to modern NCOs (Non-commissioned officers).
• Protectores Augusti Nostri (a.k.a. Protectores Divini Lateris) – Honorific title for senior officers singled out for their loyalty to the Emperor and soldierly qualities. The protectores were an order of honor rather than a military unit. The order first appeared in the mid-200s AD.
• Quaestionarius – An interrogator or torturer.
• Retentus – A soldier kept in service after serving required term.
• Rorarii – The final line, or reserve, in the ancient pre-Marius Roman army. These were removed even before the so-called "Marian reforms", as the Triarii provided a very sturdy anchor.
• Sagittarii – Archers, including horse-riding auxiliary archers recruited mainly in North Africa, Balkans, and later the Eastern Empire.
• Salararius – A soldier enjoying special service conditions or hired as a mercenary.
• Scholae – was used in the late Roman Empire to signify a unit of Imperial Guards.
• Scholae Palatinae – An elite troop of soldiers created by the Emperor Constantine the Great to provide personal protection of the Emperor and his immediate family.
• Scorpionarius – An artilleryman operating a scorpio artillery piece.
• Sesquiplicarii – A soldier issued one-and-a-half times pay, such as a Tesserarius or a minor cavalry officer as part of a Turma
• Signifer – Standard bearer of the Roman Legion.
• Simplares - A soldier paid standard pay; a regular legionaire or somebody paid the equivalent
• Socii – Troops from allied states in the pre-Marian army before the Social War (91–88 BC)
• Speculatores and Exploratores – The scouts and reconnaissance element of the Roman army.
• Supernumerarii – Supernumerary soldiers who served to fill the places of those who were killed or disabled by their wounds. Also used for the cavalry contingent of a legion during the Principate, who despite being included on the cohort lists, camped separate to the infantry.
• Strategos - General and military governor of a theme in the Byzantine Empire.
• Stratelates – A Greek translation for the rank of magister militum that was used in the late Roman and Byzantine armies.
• Stratopedarches – A term originally used to refer to a Roman camp prefect, it was later used for a Roman or Byzantine general or a Byzantine commander-in-chief.
• Tablifer – A standard-bearer for the guard cavalry.
• Tesserarius – Guard commander, one per centuria.
• Tirones – A basic trainee.
• Torquati - A soldier issued with a golden collar in reward for bravery or valor. Depending on circumstances, they may also be rewarded with double pay, making them Torquato Duplares
• Triarii – Spearmen of the pre-Marian armies, equipped with the Hasta, who formed the third line of battle behind the Principes.
• Tribuni angusticlavii – Military tribune of equestrian rank, five of whom were assigned to each legion.
• Tribunus militum - Officer in the Roman army who ranked below the legate but above the centurion.
• Tribunus militum laticlavius – Military tribune of senatorial rank. Second in command of a legion. Appointments to this rank seem to have ceased during the sole reign of Gallienus as part of a policy of excluding senators from military commands.
• Tubicen – A trumpeter.
• Urbanae – A special police force of Rome, created to counterbalance the Praetorians.
• Velites – A class of light infantry in the army of the Roman Republic.
• Venator – A hunter (a type of immunes).
• Vexillarius – Bearer of a vexillum (standard).
• Vigiles – were the firefighters and police.

Legio VII Claudia (Latin for "The 7th Claudian Legion") was a legion of the Ancient Roman army.

The Gallienus usurpers were the usurpers who claimed imperial power during the reign of Gallienus (253–268, the first part of which he shared with his father Valerian). The existence of usurpers during the Crisis of the Third Century was very common, and the high number of usurpers fought by Gallienus is due to his long rule; fifteen years being considered long by the standards of the 3rd century Roman Empire.

Egnatia Mariniana (fl. c. early 200s CE) was probably the wife of Roman Emperor Valerian and mother of Emperor Gallienus. She died before Valerian's ascension to the throne in 253.

Ingenuus was a Roman military commander, the imperial legate in Pannonia, who became a usurper to the throne of the emperor Gallienus when he led a brief and unsuccessful revolt in the year 260. Appointed by Gallienus himself, Ingenuus served him well by repulsing a Sarmatian invasion and securing the Pannonian border, at least temporarily. Ingenuus had also been charged with the military education of Caesar Cornelius Licinius Valerianus, the young son of Emperor Gallienus, but after the boy's death in 258, his position became perilous.

A well-liked and admired commander, Ingenuus found an opportunity to become the Roman Emperor when Valerian was captured and killed by Shapur I of the Sassanid Empire. Throwing off their allegiance to Valerian's son, the legions of Moesia proclaimed Ingenuus Roman Emperor at Sirmium in 260. Gallienus was in Germania on the Rhine frontier, so he acted quickly by recalling troops from Gaul and after a rapid march he met Ingenuus on the battlefield at Mursa. The troops of Ingenuus were defeated, as Gallienus' general, Aureolus, used to great effect the advantage given by the mobility of an improved cavalry component of the army, which was the remarkable military innovation wanted by the Emperor.

The Battle of Mediolanum took place in 259, between the Alemanni and the Roman legions under the command of Emperor Gallienus.

45°28′00″N 9°10′00″E / 45.466667°N 9.166667°E / 45.466667; 9.166667

P. C. Regalianus (died 260/261), known in English as Regalian, was Roman usurper for a few months in 260 and/or 261, during the Crisis of the Third Century, a period of intense political instability in the Roman Empire. Regalian was acclaimed emperor by the troops along the Danube river, a region of the empire that frequently experienced barbarian raids, probably in the hope that he might be able to secure the frontier.

Accounts by surviving literary sources concerning Regalian are brief and few in number, and are mostly considered unreliable. The Historia Augusta relates that he was of Dacian descent, and a descendant of the Dacian king Decebalus, but this is mostly rejected in modern scholarship. Regalianus was married to Sulpicia Dryantilla, a woman from a prestigious senatorial family, which instead points to Regalian also being of high-ranking Roman descent. Regalian's acclamation as emperor was in the wake of a previous usurpation attempt by Ingenuus, also proclaimed by the Danube troops, that had been defeated by emperor Gallienus (r. 253–268). Unlike Ingenuus, and revolutionary for an imperial claimant, Regalian founded his own mint at Carnuntum, his seat of power. He minted coins of himself and his wife, though they were typically of poor quality.