Caesar and the First Triumvirate

Landing of the Romans in Kent, 55 BC: Caesar with

100 ships and two legions made an opposed landing, probably near Deal. After pressing a
little way inland against fierce opposition and losing ships in a storm, he retired back across
the English Channel to Gaul from what was a reconnaissance in force, only to return the
following year for a more serious invasion.
In the mid-1st century BC, Roman politics were restless. Political divisions in Rome
split into one of two groups, populares (who hoped for the support of the people)
and optimates (the 'best', who wanted to maintain exclusive aristocratic control).
Sulla overthrew all populist leaders and his constitutional reforms removed powers
(such as those of the tribune of the plebs) that had supported populist approaches.
Meanwhile, social and economic stresses continued to build; Rome had become a
metropolis with a super-rich aristocracy, debt-ridden aspirants, and a large proletariat
often of impoverished farmers. The latter groups supported the Catilinarian
conspiracy—a resounding failure since the consul Marcus Tullius Cicero quickly
arrested and executed the main leaders.

Julius Caesar reconciled the two most powerful men in Rome: Marcus Licinius
Crassus, who had financed much of his earlier career, and Crassus' rival, Gnaeus
Pompeius Magnus (anglicised as Pompey), to whom he married his daughter. He
formed them into a new informal alliance including himself, the First
Triumvirate ('three men'). Caesar's daughter died in childbirth in 54 BC, and in
53 BC, Crassus invaded Parthia and was killed in the Battle of Carrhae; the
Triumvirate disintegrated. Caesar conquered Gaul, obtained immense wealth,
respect in Rome and the loyalty of battle-hardened legions. He became a threat to
Pompey and was loathed by many optimates. Confident that Caesar could be
stopped by legal means, Pompey's party tried to strip Caesar of his legions, a
prelude to Caesar's trial, impoverishment, and exile.

To avoid this fate, Caesar crossed the Rubicon River and invaded Rome in 49 BC.
The Battle of Pharsalus was a brilliant victory for Caesar and in this and other
campaigns, he destroyed all of the optimates leaders: Metellus Scipio, Cato the
Younger, and Pompey's son, Gnaeus Pompeius Magnus. Pompey was murdered in
Egypt in 48 BC. Caesar was now pre-eminent over Rome: in five years he held four
consulships, two ordinary dictatorships, and two special dictatorships, one for
perpetuity. He was murdered in 44 BC, on the Ides of March by the Liberatores.[41]
Octavian and the Second Triumvirate
Caesar's assassination caused political and social turmoil in Rome; the city was
ruled by his friend and colleague, Mark Antony. Soon afterward, Octavian, whom
Caesar adopted through his will, arrived in Rome. Octavian (historians regard
Octavius as Octavian due to the Roman naming conventions) tried to align himself
with the Caesarian faction. In 43 BC, along with Antony and Marcus Aemilius
Lepidus, Caesar's best friend,[42] he legally established the Second Triumvirate. Upon
its formation, 130–300 senators were executed, and their property was confiscated,
due to their supposed support for the Liberatores.[43]

In 42 BC, the Senate deified Caesar as Divus Iulius; Octavian thus became Divi
filius,[44] the son of the deified. In the same year, Octavian and Antony defeated both
Caesar's assassins and the leaders of the Liberatores, Marcus Junius
Brutus and Gaius Cassius Longinus, in the Battle of Philippi. The Second Triumvirate
was marked by the proscriptions of many senators and equites: after a revolt led by
Antony's brother Lucius Antonius, more than 300 senators and equites involved were
executed, although Lucius was spared.[45]

The Triumvirate divided the Empire among the triumvirs: Lepidus was given charge
of Africa, Antony, the eastern provinces, and Octavian remained in Italia and
controlled Hispania and Gaul. The Second Triumvirate expired in 38 BC but was
renewed for five more years. However, the relationship between Octavian and
Antony had deteriorated, and Lepidus was forced to retire in 36 BC after betraying
Octavian in Sicily. By the end of the Triumvirate, Antony was living in Ptolemaic
Egypt, ruled by his lover, Cleopatra VII. Antony's affair with Cleopatra was seen as
an act of treason, since she was queen of another country. Additionally, Antony
adopted a lifestyle considered too extravagant and Hellenistic for a Roman
statesman.[46] Following Antony's Donations of Alexandria, which gave to
Cleopatra the title of "Queen of Kings", and to Antony's and Cleopatra's children the
regal titles to the newly conquered Eastern territories, war between Octavian and
Antony broke out. Octavian annihilated Egyptian forces in the Battle of Actium in
31 BC. Antony and Cleopatra committed suicide. Now Egypt was conquered by the
Roman Empire.

Empire – the Principate

Main article: Roman Empire
 The Augustus of Prima Porta, 1st century AD,
depicting Augustus, the first Roman emperor
In 27 BC and at the age of 36, Octavian was the sole Roman leader. In that year, he
took the name Augustus. That event is usually taken by historians as the beginning
of Roman Empire. Officially, the government was republican, but Augustus assumed
absolute powers.[47] His reform of the government brought about a two-century period
colloquially referred to by Romans as the Pax Romana.

Julio-Claudian dynasty
The Julio-Claudian dynasty was established by Augustus. The emperors of this
dynasty were Augustus, Tiberius, Caligula, Claudius and Nero. The Julio-Claudians
started the destruction of republican values, but on the other hand, they boosted
Rome's status as the central power in the Mediterranean region.[48] While Caligula
and Nero are usually remembered in popular culture as dysfunctional emperors,
Augustus and Claudius are remembered as successful in politics and the military.
This dynasty instituted imperial tradition in Rome[49] and frustrated any attempt to
reestablish a Republic.[50]

Augustus (r. 27 BC – AD 14) gathered almost all the republican powers under his
official title, princeps, and diminished the political influence of the senatorial class by
boosting the equestrian class. The senators lost their right to rule certain provinces,
like Egypt, since the governor of that province was directly nominated by the
emperor. The creation of the Praetorian Guard and his reforms in the military,
creating a standing army with a fixed size of 28 legions, ensured his total control
over the army.[51] Compared with the Second Triumvirate's epoch, Augustus' reign
as princeps was very peaceful, which led the people and the nobles of Rome to
support Augustus, increasing his strength in political affairs.[52] His generals were
responsible for the field command, gaining such commanders as Marcus Vipsanius
Agrippa, Nero Claudius Drusus and Germanicus much respect from the populace
and the legions. Augustus intended to extend the Roman Empire to the whole known
world, and in his reign, Rome
conquered Cantabria, Aquitania, Raetia, Dalmatia, Illyricum and Pannonia.[53] Under
Augustus' reign, Roman literature grew steadily in what is known as the Golden Age
of Latin Literature. Poets like Virgil, Horace, Ovid and Rufus developed a rich
literature, and were close friends of Augustus. Along with Maecenas, he sponsored
patriotic poems, such as Virgil's epic Aeneid and historiographical works like those
of Livy. Augustus continued the changes to the calendar promoted by Caesar, and
the month of August is named after him.[54] Augustus brought a peaceful and thriving
era to Rome, known as Pax Romana.

Extent of the Roman Empire

under Augustus. The yellow legend represents the extent of the Republic in 31 BC, the
shades of green represent gradually conquered territories under the reign of Augustus, and
pink areas on the map represent client states; areas under Roman control shown here were
subject to change even during Augustus' reign, especially in Germania.
The Julio-Claudians continued to rule Rome after Augustus' death in 14 AD and
remained in power until the death of Nero in 68 AD.[55] Influenced by his wife, Livia
Drusilla, Augustus appointed her son from another marriage, Tiberius, as his heir.
[56]
The Senate agreed with the succession, and granted to Tiberius the same titles
and honours once granted to Augustus: the title of princeps and Pater patriae, and
the Civic Crown. However, Tiberius was not an enthusiast for political affairs: after
agreement with the Senate, he retired to Capri in 26 AD,[57] and left control of the city
of Rome in the hands of the praetorian prefect Sejanus (until 31 AD)
and Macro (from 31 to 37 AD).

Tiberius died (or was killed)[58] in 37 AD. The male line of the Julio-Claudians was
limited to Tiberius' nephew Claudius, his grandson Tiberius Gemellus and his grand-
nephew Caligula. As Gemellus was still a child, Caligula was chosen to rule the
empire. He was a popular leader in the first half of his reign, but became a crude and
insane tyrant in his years controlling government.[59] The Praetorian Guard murdered
Caligula four years after the death of Tiberius,[60] and, with belated support from the
senators, proclaimed his uncle Claudius as the new emperor.[61] Claudius was not as
authoritarian as Tiberius and Caligula. Claudius conquered Lycia and Thrace; his
most important deed was the beginning of the conquest of Britannia.[62] Claudius was
poisoned by his wife, Agrippina the Younger in 54 AD.[63] His heir was Nero, son of
Agrippina and her former husband, since Claudius' son Britannicus had not reached
manhood upon his father's death.

Nero sent his general, Suetonius Paulinus, to invade modern-day Wales, where he
encountered stiff resistance. The Celts there were independent, tough, resistant to
tax collectors, and fought Paulinus as he battled his way across from east to west. It
took him a long time to reach the north-west coast, and in 60 AD he finally crossed
the Menai Strait to the sacred island of Mona (Anglesey), the last stronghold of
the druids.[64] His soldiers attacked the island and massacred the druids: men, women
and children,[65] destroyed the shrine and the sacred groves and threw many of the
sacred standing stones into the sea. While Paulinus and his troops were massacring
druids in Mona, the tribes of modern-day East Anglia staged a revolt led by
queen Boadicea of the Iceni.[66] The rebels sacked and
burned Camulodunum, Londinium and Verulamium (modern-day Colchester, London
and St Albans respectively) before they were crushed by Paulinus.[67] Boadicea,
like Cleopatra before her, committed suicide to avoid the disgrace of being paraded
in triumph in Rome.[68] Nero is widely known as the first persecutor of Christians and
for the Great Fire of Rome, rumoured to have been started by the emperor himself.
[69]
A conspiracy against Nero in 65 AD under Calpurnius Piso failed, but in 68 AD the
armies under Julius Vindex in Gaul and Servius Sulpicius Galba in modern-day
Spain revolted. Deserted by the Praetorian Guards and condemned to death by the
senate, Nero killed himself.[70]

Flavian dynasty

Bust of Vespasian, founder of the Flavian dynasty

The Flavians were the second dynasty to rule Rome.[71] By 68 AD, the year of Nero's
death, there was no chance of a return to the Republic, and so a new emperor had
to arise. After the turmoil in the Year of the Four Emperors, Titus Flavius
Vespasianus (anglicised as Vespasian) took control of the empire and established a
new dynasty. Under the Flavians, Rome continued its expansion, and the state
remained secure.[72] Under Trajan, the Roman Empire reached the peak of its
territorial expansion.[73] Rome's dominion now spanned 5.0 million square kilometres
(1.9 million square miles).[2]

The most significant military campaign undertaken during the Flavian period was
the siege and destruction of Jerusalem in 70 AD by Titus. The destruction of the city
was the culmination of the Roman campaign in Judea following the Jewish uprising
of 66 AD. The Second Temple was completely demolished, after which Titus'
soldiers proclaimed him imperator in honour of the victory. Jerusalem was sacked
and much of the population killed or dispersed. Josephus claims that 1,100,000
people were killed during the siege, of whom a majority were Jewish.[74] 97,000 were
captured and enslaved. Many fled to areas around the Mediterranean.

Vespasian was a general under Claudius and Nero and fought as a commander in
the First Jewish-Roman War. Following the turmoil of the Year of the Four Emperors,
in 69 AD, four emperors were enthroned in turn: Galba, Otho, Vitellius, and, lastly,
Vespasian, who crushed Vitellius' forces and became emperor.[75] He reconstructed
many buildings which were uncompleted, like a statue of Apollo and the temple
of Divus Claudius ("the deified Claudius"), both initiated by Nero. Buildings destroyed
by the Great Fire of Rome were rebuilt, and he revitalised the Capitol. Vespasian
started the construction of the Flavian Amphitheater, commonly known as
the Colosseum.[75] The historians Josephus and Pliny the Elder wrote their works
during Vespasian's reign. Vespasian was Josephus' sponsor and Pliny dedicated
his Naturalis Historia to Titus, son of Vespasian. Vespasian sent legions to defend
the eastern frontier in Cappadocia, extended the occupation in Britannia (modern-
day England, Wales and southern Scotland) and reformed the tax system. He died in
79 AD.

Titus became emperor in 79. He finished the Flavian Amphitheater, using war spoils
from the First Jewish-Roman War, and hosted victory games that lasted for a
hundred days. These games included gladiatorial combats, horse races and a
sensational mock naval battle on the flooded grounds of the Colosseum.[76] Titus died
of fever in 81 AD, and was succeeded by his brother Domitian. As emperor,
Domitian showed the characteristics of a tyrant.[77] He ruled for fifteen years, during
which time he acquired a reputation for self-promotion as a living god. He
constructed at least two temples in honour of Jupiter, the supreme deity in Roman
religion.[78] He was murdered following a plot within his own household.

Nerva–Antonine dynasty

The Roman Empire reached its greatest extent

under Trajan in AD 117
Following Domitian's murder, the Senate rapidly appointed Nerva as Emperor. Nerva
had noble ancestry, and he had served as an advisor to Nero and the Flavians. His
rule restored many of the traditional liberties of Rome's upper classes, which
Domitian had over-ridden.[79] The Nerva–Antonine dynasty from 96 AD to 192 AD
included the "five good emperors" Nerva, Trajan, Hadrian, Antoninus
Pius and Marcus Aurelius. Trajan, Hadrian, Antoninus Pius and Marcus Aurelius
were part of Italic families settled in Roman colonies outside of Italy: the families of
Trajan and Hadrian had settled in Italica (Hispania Baetica), that of Antoninus Pius
in Colonia Agusta Nemausensis (Gallia Narbonensis), and that of Marcus Aurelius
in Colonia Claritas Iulia Ucubi (Hispania Baetica). The Nerva-Antonine dynasty came
to an end with Commodus, son of Marcus Aurelius.[80]

Nerva abdicated and died in 98 AD, and was succeeded by the general Trajan.
Trajan is credited with the restoration of traditional privileges and rights of commoner
and senatorial classes, which later Roman historians claim to have been eroded
during Domitian's autocracy.[81] Trajan fought three Dacian wars, winning territories
roughly equivalent to modern-day Romania and Moldova. He undertook an
ambitious public building program in Rome, including Trajan's Forum, Trajan's
Market and Trajan's Column, with the architect Apollodorus of Damascus. He
remodelled the Pantheon and extended the Circus Maximus.
[82]
When Parthia appointed a king for Armenia without consulting Rome, Trajan
declared war on Parthia and deposed the king of Armenia. In 115 he took the
Northern Mesopotamian cities of Nisibis and Batnae, organised a province
of Mesopotamia (116), and issued coins that claimed Armenia and Mesopotamia
were under the authority of the Roman people.[83] In that same year, he
captured Seleucia and the Parthian capital Ctesiphon (near modern Baghdad).
[84]
After defeating a Parthian revolt and a Jewish revolt, he withdrew due to health
issues, and in 117, he died of edema.

Map showing the location of Hadrian's Wall and

the Antonine Wall in Scotland and Northern England
Trajan's successor Hadrian withdrew all the troops stationed in Parthia, Armenia and
Mesopotamia (modern-day Iraq), abandoning Trajan's conquests. Hadrian's army
crushed a revolt in Mauretania and the Bar Kokhba revolt in Judea. This was the last
large-scale Jewish revolt against the Romans, and was suppressed with massive
repercussions in Judea. Hundreds of thousands of Jews were killed. Hadrian
renamed the province of Judea "Provincia Syria Palaestina", after one of Judea's
most hated enemies.[85] He constructed fortifications and walls, like the
celebrated Hadrian's Wall which separated Roman Britannia and the tribes of
modern-day Scotland. Hadrian promoted culture, especially the Greek. He
forbade torture and humanised the laws. His many building projects included
aqueducts, baths, libraries and theatres; additionally, he travelled nearly every
province in the Empire to review military and infrastructural conditions.[86]

Following Hadrian's death in 138 AD, his successor Antoninus Pius built temples,
theatres, and mausoleums, promoted the arts and sciences, and bestowed honours
and financial rewards upon the teachers of rhetoric and philosophy. On becoming
emperor, Antoninus made few initial changes, leaving intact as far as possible the
arrangements instituted by his predecessor. Antoninus expanded Roman Britannia
by invading what is now southern Scotland and building the Antonine Wall.[87] He also
continued Hadrian's policy of humanising the laws. His reign was the most peaceful
in the entire history of Roman Empire, he left "an empire in very fine shape. It was a
height that, arguably, it would never reach again."[88] He died in 161 AD.

The Pantheon, Rome, built during the reign

of Hadrian, which still contains the largest unreinforced concrete dome in the world
Marcus Aurelius, known as the Philosopher, was the last of the Five Good Emperors.
He was a stoic philosopher and wrote the Meditations. He defeated barbarian tribes
in the Marcomannic Wars as well as the Parthian Empire.[89] His co-emperor, Lucius
Verus, died in 169 AD, probably from the Antonine Plague, a pandemic that killed
nearly five million people through the Empire in 165–180 AD.[90]

From Nerva to Marcus Aurelius, the empire achieved an unprecedented status. The
powerful influence of laws and manners had gradually cemented the union of the
provinces. All the citizens enjoyed and abused the advantages of wealth. The image
of a free constitution was preserved with decent reverence. The Roman senate
appeared to possess the sovereign authority, and devolved on the emperors all the
executive powers of government. Gibbon declared the rule of these "Five Good
Emperors" the golden era of the Empire.[91] During this time, Rome reached its
greatest territorial extent.[92]

Commodus, son of Marcus Aurelius, became emperor after his father's death. He is
not counted as one of the Five Good Emperors, due to his direct kinship with the
latter emperor; in addition, he was militarily passive. Cassius Dio identifies his reign
as the beginning of Roman decadence: "(Rome has transformed) from a kingdom of
gold to one of iron and rust."[89]

Severan dynasty
Commodus was killed by a conspiracy involving Quintus Aemilius Laetus and his
wife Marcia in late 192 AD. The following year is known as the Year of the Five
Emperors, during which Helvius Pertinax, Didius Julianus, Pescennius Niger, Clodius
Albinus and Septimius Severus held the imperial dignity. Pertinax, a member of the
senate who had been one of Marcus Aurelius's right-hand men, was the choice of
Laetus, and he ruled vigorously and judiciously. Laetus soon became jealous and
instigated Pertinax's murder by the Praetorian Guard, who then auctioned the empire
to the highest bidder, Didius Julianus, for 25,000 sesterces per man.[93] The people of
Rome were appalled and appealed to the frontier legions to save them. The legions
of three frontier provinces—Britannia, Pannonia Superior, and Syria—resented being
excluded from the "donative" and replied by declaring their individual generals to be
emperor. Lucius Septimius Severus Geta, the Pannonian commander, bribed the
opposing forces, pardoned the Praetorian Guards and installed himself as emperor.
He and his successors governed with the legions' support. The changes
on coinage and military expenditures were the root of the financial crisis that marked
the Crisis of the Third Century.
 The Severan Tondo, c. 199, Severus, Julia Domna,
Caracalla and Geta, whose face is erased
Severus was enthroned after invading Rome and having Didius Julianus killed.
Severus attempted to revive totalitarianism and, addressing the Roman people and
Senate, praised the severity and cruelty of Marius and Sulla, which worried the
senators.[94] When Parthia invaded Roman territory, Severus successfully waged war
against that country. Notwithstanding this military success, Severus failed in
invading Hatra, a rich Arabian city. Severus killed his legate, who was gaining
respect from the legions; and his soldiers fell victim to famine. After this disastrous
campaign, he withdrew.[95] Severus also intended to vanquish the whole of Britannia.
To achieve this, he waged war against the Caledonians. However, he became ill and
died in 211 AD.

Bust of Caracalla from the Capitoline Museums, Rome

His sons Caracalla and Geta were made emperors. Caracalla had his brother, a
youth, assassinated in his mother's arms, and may have murdered 20,000 of Geta's
followers. Like his father, Caracalla was warlike. He continued Severus' policy and
gained respect from the legions. Knowing that the citizens of Alexandria disliked him
and were denigrating his character, Caracalla served a banquet for its notable
citizens, after which his soldiers killed all the guests. From the security of the temple
of Sarapis, he then directed an indiscriminate slaughter of Alexandria's people.[96] In
212, he issued the Edict of Caracalla, giving full Roman citizenship to all free men
living in the Empire, with the exception of the dediticii, people who had become
subject to Rome through surrender in war, and freed slaves.[97]

Mary Beard points to the edict as a fundamental turning point, after which Rome was
"effectively a new state masquerading under an old name".[98]

Macrinus conspired to have Caracalla assassinated by one of his soldiers during a

pilgrimage to the Temple of the Moon in Carrhae, in 217 AD. Macrinus assumed
power, but soon removed himself from Rome to the east and Antioch. His brief reign
ended in 218, when the youngster Bassianus, high priest of the temple of the Sun at
Emesa, and supposedly illegitimate son of Caracalla, was declared Emperor by the
disaffected soldiers of Macrinus. He adopted the name of Antoninus but history has
named him after his Sun god Elagabalus, represented on Earth in the form of a large
black stone. An incompetent and lascivious ruler,[99] Elagabalus adopted his
cousin Severus Alexander, as Caesar, but subsequently grew jealous and attempted
to assassinate him. However, the Praetorian guard preferred Alexander, murdered
Elagabalus, dragged his mutilated corpse through the streets of Rome, and threw it
into the Tiber. Severus Alexander then succeeded him. Alexander waged war
against many foes, including the revitalised Persia and also the Germanic peoples,
who invaded Gaul. His losses generated dissatisfaction among his soldiers, and
some of them murdered him during his Germanic campaign in 235 AD.[100]

Crisis of the Third Century

Main article: Crisis of the Third Century

The Roman Empire suffered

internal schisms, forming the Palmyrene Empire and the Gallic Empire
A disastrous scenario emerged after the death of Alexander Severus: the Roman
state was plagued by civil wars, external invasions, political
chaos, pandemics and economic depression.[101] The old Roman values had fallen,
and Mithraism and Christianity had begun to spread through the populace. Emperors
were no longer men linked with nobility; they usually were born in lower-classes of
distant parts of the Empire. These men rose to prominence through military ranks,
and became emperors through civil wars.

There were 26 emperors in a 49-year period, a signal of political

instability. Maximinus Thrax was the first ruler of that time, governing for just three
years. Others ruled just for a few months, like Gordian I, Gordian
II, Balbinus and Hostilian. The population and the frontiers were abandoned, since
the emperors were mostly concerned with defeating rivals and establishing their
power. The economy also suffered: massive military expenditures from
the Severi caused a devaluation of Roman coins. Hyperinflation came at this time as
well. The Plague of Cyprian broke out in 250 and killed a huge portion of the
population.[102] In 260 AD, the provinces of Syria Palaestina, Asia
Minor and Egypt separated from the rest of the Roman state to form the Palmyrene
Empire, ruled by Queen Zenobia and centered on Palmyra. In that same year
the Gallic Empire was created by Postumus, retaining Britannia and Gaul.[103] These
countries separated from Rome after the capture of emperor Valerian by
the Sassanids of Persia, the first Roman ruler to be captured by his enemies; it was
a humiliating fact for the Romans.[102] The crisis began to recede during the reigns
of Claudius Gothicus (268–270), who defeated the Gothic invaders,
and Aurelian (271–275), who reconquered both the Gallic and Palmyrene Empires.
[104]
The crisis was overcome during the reign of Diocletian.

Empire – The Tetrarchy

Main article: Tetrarchy
Diocletian

A Roman follis depicting the profile of Diocletian

In 284 AD, Diocletian was hailed as Imperator by the eastern army. Diocletian
healed the empire from the crisis, by political and economic shifts. A new form of
government was established: the Tetrarchy. The Empire was divided among four
emperors, two in the West and two in the East. The first tetrarchs were Diocletian (in
the East), Maximian (in the West), and two junior emperors, Galerius (in the East)
and Flavius Constantius (in the West). To adjust the economy, Diocletian made
several tax reforms.[105]

Diocletian expelled the Persians who plundered Syria and conquered some
barbarian tribes with Maximian. He adopted many behaviours of Eastern monarchs.
Anyone in the presence of the emperor had now to prostrate himself—a common act
in the East, but never practised in Rome before.[106] Diocletian did not use a disguised
form of Republic, as the other emperors since Augustus had done.[107] Between 290
and 330, half a dozen new capitals had been established by the members of the
Tetrarchy, officially or not: Antioch, Nicomedia, Thessalonike, Sirmium, Milan, and
Trier.[108] Diocletian was also responsible for a significant Christian persecution. In 303
he and Galerius started the persecution and ordered the destruction of all the
Christian churches and scripts and forbade Christian worship.[109] Diocletian abdicated
in 305 AD together with Maximian, thus, he was the first Roman emperor to resign.
His reign ended the traditional form of imperial rule, the Principate (from princeps)
and started the Tetrarchy.

The Aula Palatina of Trier, Germany (then part of

the Roman province of Gallia Belgica), a Christian basilica built during the reign
of Constantine I (r. 306–337 AD)
Constantine and Christianity
Constantine assumed the empire as a tetrarch in 306. He conducted many wars
against the other tetrarchs. Firstly he defeated Maxentius in 312. In 313, he issued
the Edict of Milan, which granted liberty for Christians to profess their religion.
[110]
Constantine was converted to Christianity, enforcing the Christian faith. He began
the Christianization of the Empire and of Europe—a process concluded by the
Catholic Church in the Middle Ages. He was defeated by the Franks and
the Alamanni during 306–308. In 324 he defeated another tetrarch, Licinius, and
controlled all the empire, as it was before Diocletian. To celebrate his victories and
Christianity's relevance, he rebuilt Byzantium and renamed it Nova Roma ("New
Rome"); but the city soon gained the informal name of Constantinople ("City of
Constantine").[111]

The reign of Julian, who under the influence of his adviser Mardonius attempted to
restore Classical Roman and Hellenistic religion, only briefly interrupted the
succession of Christian emperors. Constantinople served as a new capital for the
Empire. In fact, Rome had lost its central importance since the Crisis of the Third
Century—Mediolanum was the western capital from 286 to 330, until the reign
of Honorius, when Ravenna was made capital, in the 5th century.[112] Constantine's
administrative and monetary reforms, that reunited the Empire under one emperor,
and rebuilt the city of Byzantium, as Constantinopolis Nova Roma, changed the high
period of the ancient world.

Fall of the Western Roman Empire

Main article: Fall of the Western Roman Empire
In the late 4th and 5th centuries the Western Empire entered a critical stage which
terminated with the fall of the Western Roman Empire.[113] Under the last emperors of
the Constantinian dynasty and the Valentinianic dynasty, Rome lost decisive battles
against the Sasanian Empire and Germanic barbarians: in 363, emperor Julian the
Apostate was killed in the Battle of Samarra, against the Persians and the Battle of
Adrianople cost the life of emperor Valens (364–378); the victorious Goths were
never expelled from the Empire nor assimilated.[114] The next emperor, Theodosius
I (379–395), gave even more force to the Christian faith, and after his death, the
Empire was divided into the Eastern Roman Empire, ruled by Arcadius and
the Western Roman Empire, commanded by Honorius, both of which were
Theodosius' sons.[115]
Ending invasions on Roman Empire between AD 100–500. Visigoths entering Athens. The Sack
of Rome by the Barbarians in 410 by Joseph-Noël Sylvestre.
The situation became more critical in 408, after the death of Stilicho, a general who
tried to reunite the Empire and repel barbarian invasion in the early years of the 5th
century. The professional field army collapsed. In 410, the Theodosian dynasty saw
the Visigoths sack Rome.[116] During the 5th century, the Western Empire experienced
a significant reduction of its territory. The Vandals conquered North Africa,
the Visigoths claimed the southern part of Gaul, Gallaecia was taken by
the Suebi, Britannia was abandoned by the central government, and the Empire
suffered further from the invasions of Attila, chief of the Huns.
[117]
General Orestes refused to meet the demands of the barbarian "allies" who now
formed the army, and tried to expel them from Italy. Unhappy with this, their
chieftain Odoacer defeated and killed Orestes, invaded Ravenna and
dethroned Romulus Augustus, son of Orestes. This event of 476, usually marks the
end of Classical antiquity and beginning of the Middle Ages.[118] The Roman noble
and former emperor Julius Nepos continued to rule as emperor from Dalmatia even
after the deposition of Romulus Augustus until his death in 480. Some historians
consider him to be the last emperor of the Western Empire instead of Romulus
Augustus.[119]

After 1200 years of independence and nearly 700 years as a great power, the rule of
Rome in the West ended.[120] Various reasons for Rome's fall have been proposed,
including loss of Republicanism, moral decay, military tyranny, class war, slavery,
economic stagnation, environmental change, disease, the decline of the Roman
race, as well as the inevitable ebb and flow that all civilisations experience. The
Eastern Empire survived for almost 1000 years after the fall of its Western
counterpart and became the most stable Christian realm during the Middle Ages.
During the 6th century, Justinian reconquered the Italian peninsula from the
Ostrogoths, North Africa from the Vandals, and southern Hispania from the
Visigoths. But within a few years of Justinian's death, Byzantine possessions in Italy
were greatly reduced by the Lombards who settled in the peninsula.[121] In the east,
partially due to the weakening effect of the Plague of Justinian as well as a series of
mutually destructive wars against the Persian Sassanian Empire, the Byzantines
were threatened by the rise of Islam. Its followers rapidly brought about the conquest
of the Levant, the conquest of North Africa and the conquest of Egypt during
the Arab–Byzantine wars, and soon presented a direct threat to Constantinople.[122]
[123]
In the following century, the Arabs captured southern Italy and Sicily.[124] In the
west, Slavic populations penetrated deep into the Balkans.

The Byzantine Romans, however, managed to stop further Islamic expansion into
their lands during the 8th century and, beginning in the 9th century, reclaimed parts
of the conquered lands.[122][125] In 1000 AD, the Eastern Empire was at its height: Basil
II reconquered Bulgaria and Armenia, and culture and trade flourished.[126] However,
soon after, this expansion was abruptly stopped in 1071 with the Byzantine defeat in
the Battle of Manzikert. The aftermath of this battle sent the empire into a protracted
period of decline. Two decades of internal strife and Turkic invasions ultimately led
Emperor Alexios I Komnenos to send a call for help to the Western European
kingdoms in 1095.[122] The West responded with the Crusades, eventually resulting in
the Sack of Constantinople by participants of the Fourth Crusade. The conquest of
Constantinople in 1204 fragmented what remained of the Empire into successor
states; the ultimate victor was the Empire of Nicaea.[127] After the recapture of
Constantinople by Imperial forces, the Empire was little more than a Greek state
confined to the Aegean coast. The Eastern Roman (Byzantine) Empire collapsed
when Mehmed the Conqueror conquered Constantinople on 29 May 1453.[128]