The Western Roman Empire refers to the western half of the Roman Empire, from its division by Diocletian in 285; the other half of the Roman Empire was the Eastern Roman Empire, today widely known as the Byzantine Empire.
Rome ceased to be the capital from the time of the division. In 286, the capital of the Western Roman Empire became Mediolanum (modern Milan). In 402, the capital was again moved, this time to Ravenna.
The Western Empire existed intermittently in several periods between the 3rd century and 5th century, after Diocletian's Tetrarchy and the reunifications associated with Constantine the Great and Julian the Apostate (324-363). Theodosius I (379-395) was the last Roman Emperor who ruled over a unified Roman empire. After his death in 395, the Roman Empire was permanently divided. The Western Roman Empire ended officially with the abdication of Romulus Augustus under pressure of Odoacer on 4 September 476, and unofficially with the death of Julius Nepos in 480.
Despite a brief period of reconquest by its counterpart, the Eastern Roman Empire, the Western Roman Empire would not rise again. As the Western Roman Empire fell, a new era began in Western European history: the Middle Ages and more specifically the Dark Ages.
Prior to the establishment of the Empire, the territories of the Roman Republic had been divided among the Second Triumvirate, composed of Octavian, Mark Antony, and Marcus Aemilius Lepidus. Antony received the provinces in the East: Achaea, Macedonia and Epirus (roughly modern Greece), Bithynia, Pontus and Asia (roughly modern Turkey), Syria, Cyprus and Cyrenaica. These lands had previously been conquered by Alexander the Great; thus, much of the aristocracy was of Greek origin. The whole region, especially the major cities, had been largely assimilated into Greek culture, Greek often serving as the lingua-franca.
Octavian, on the other hand, obtained the Roman provinces of the West: Italia (modern Italy), Gaul (modern France), Gallia Belgica (parts of modern Belgium, the Netherlands and Luxembourg) and Hispania (modern Spain and Portugal). These lands also included Greek and Carthaginian colonies in the coastal areas, though Celtic tribes such as Gauls and Celtiberians were culturally dominant.
Upon the defeat of Mark Antony, a victorious Octavian controlled a united Roman Empire. While the Roman Empire featured many distinct cultures, all were often said to experience gradual Romanization. While the predominantly Greek culture of the East and the predominantly Latin culture of the West functioned effectively as an integrated whole, political and military developments would ultimately realign the Empire along those cultural and linguistic lines.
In a full-blown military campaign, the legions, under generals such as Vespasian, were far more numerous. To ensure a commander's loyalty, a pragmatic emperor might hold some members of the general's family hostage. To this end, Nero effectively held Domitian and Quintus Petillius Cerialis, governor of Ostia, who were respectively the younger son and brother-in-law of Vespasian. The rule of Nero ended only with the revolt of the Praetorian Guard, who had been bribed in the name of Galba. The Praetorian Guard, a figurative "sword of Damocles", were often perceived as being of dubious loyalty. Following their example, the legions at the borders increasingly participated in the civil wars.
Parthia, in the East, on the other hand, was too remote and powerful to be conquered. Any Parthian invasion was confronted and usually defeated, and the Parthians similarly repelled any Roman invasion, creating a stalemate situation.
Controlling the western border of Rome was reasonably easy, because it was relatively near, but controlling both frontiers at the same time during wartime was difficult. If the emperor was near the border in the East, chances were high that an ambitious general would rebel in the West and vice-versa, making the Empire doubly vulnerable. This wartime opportunism plagued many ruling emperors, and indeed paved the road to power for several future emperors.
Starting on 18 March 235, with the assassination of the Emperor Alexander Severus, the Roman Empire sank into a 50-year civil war, known today as the Crisis of the Third Century. The rise of the bellicose Sassanid dynasty in Parthia posed a major threat to Rome in the east. Demonstrating the increased danger, Emperor Valerian was captured by Shapur I in 259. His eldest son and heir-apparent, Gallienus, succeeded and took up the fight on the eastern frontier. Gallienus' son, Saloninus, and the Praetorian Prefect Silvanus, were residing in Colonia Agrippina (modern Cologne) to solidify the loyalty of the local legions. Nevertheless, Marcus Cassianius Latinius Postumus, the local governor of the German provinces, rebelled; his assault on Colonia Agrippina resulted in the deaths of Saloninus and the prefect. In the confusion that followed, an independent state known as the Gallic Empire emerged.
Its capital was Augusta Treverorum (modern Trier), and it quickly expanded its control over the German and Gaulish provinces and over all of Hispania and Britannia. It had its own senate, and a partial list of its consuls still survives. It maintained Roman religion, language, and culture, and was far more concerned with fighting the Germanic tribes than other Romans. However, in the reign of Claudius Gothicus (268 to 270), large expanses of the Gallic Empire were restored to Roman rule.
In 272, Emperor Aurelian finally managed to subdue Palmyra and reclaim its territory for the empire. With the East secure, he turned his attention to the West, taking the Gallic Empire a year later. Because of a secret deal between Aurelian and Gallic Emperor Tetricus I and his son Tetricus II, the Gallic army was swiftly defeated. In exchange, Aurelian spared their lives and gave the two former rebels important positions in Italy.
The external borders were mostly quiet for the remainder of the Crisis of the Third Century, although between the death of Aurelian in 275 and the accession of Diocletian ten years later, at least eight emperors or would-be emperors were killed, many assassinated by their own troops.
Under Diocletian, the political division of the Roman Empire began. In 286, through the creation of the Tetrarchy, he gave the western part to Maximian as Augustus and named Constantius Chlorus as his subordinate (Caesar). This system effectively divided the empire into four parts and created separate capitals besides Rome as a way to avoid the civil unrest that had marked the 3rd century. In the West, the capitals were Maximian's Mediolanum (now Milan) and Constantius' Trier. On 1 May 305, the two senior Augusti stepped down and were replaced by their respective Caesars.
The Tetrarchy was dead, but the idea of dividing the Roman Empire between two emperors had been validated. Very strong emperors would reunite it under their single rule, but with their death the Roman Empire would be divided again and again between the East and the West.
Constantius II focused most of his power in the East, and is often regarded as the first emperor of the Byzantine Empire. Under his rule, the city of Byzantium, only recently refounded as Constantinople, was fully developed as a capital.
In 361, Constantius II became ill and died, and Constantius Chlorus' grandson Julian, who had served as Constantius II's Caesar, took power. Julian was killed carrying on Constantius II's war against Persia in 363 and was replaced by Jovian who ruled only until 364.
More than in the East, there was also opposition to the Christianizing policy of the emperors in the western half of the empire. In 379 Valentinian I's son and successor Gratian declined to wear the mantle of pontifex maximus, and in 382 he rescinded the rights of pagan priests and removed the pagan altar from the Roman Curia, a decision which caused dissatisfaction among the traditionally pagan aristocracy of Rome.
The political situation was unstable. In 383, a powerful and popular general named Magnus Maximus seized power in the west and forced Gratian's son Valentinian II to flee to the east for aid; the Eastern Emperor Theodosius I promptly restored him to power. He also caused a ban on the native paganism to be implemented in the west in 399, enforcing Christianity. In 392 the Frankish and pagan magister militum Arbogast assassinated Valentinian II and proclaimed an obscure senator named Eugenius as emperor. The rebellion was overcome in 394 by Theodosius I, who then shortly ruled a united Empire until his death in 395. This was the last instance in which a single ruler ruled both parts of the Roman Empire; his sons, Honorius and Arcadius, were given the western and eastern half, respectively. Still minors, they were placed under the tutelage of the semi-barbarian magister militum Flavius Stilicho.
Stilicho ably defended Italy against the invading Goths, but he became a victim of court intrigues in Ravenna (where the imperial court resided since 402) and was executed for high treason in 408. In the preceding year Vandals, Alans and Suevi had invaded Gaul in massive numbers, and while the East began a slow recovery and consolidation, the West began to collapse entirely.
As the central power weakened, the State lost control of its borders and provinces, as well as control over the Mediterranean Sea. Roman Emperors tried to maintain control of the sea, but once the Vandals conquered North Africa, imperial authorities had to cover too much ground with too few resources. In many places the Roman institutions collapsed along with the economic stability. In some regions, such as Gaul and Italy, the settlement of barbarians on former Roman lands seems to have caused relatively little disruption, whereas elsewhere, notably in certain parts of North Africa, the Roman landowners were expelled and their lands confiscated.
Honorius' death in 423 was followed by turmoil until the Eastern Roman government with the force of arms installed Valentinian III as Western Emperor in Ravenna, with Galla Placidia acting as regent during her son's minority. After a violent struggle with several rivals, and against Placidia's wish, Aetius rose to the rank of magister militum. Aetius was able to stabilize the empire's military situation somewhat, relying heavily on his Hunnic allies. With their help he defeated the Burgundians, who had occupied part of southern Gaul after 407, and settled them in Savoy as Roman allies (433). Later that century, as Roman power faded away, the Burgundians extended their rule to the Rhone valley.
Meanwhile, pressure from the Visigoths and a rebellion by the governor of Africa, Bonifacius, had induced the Vandals under their king Gaiseric to cross over from Spain in 429. They temporarily halted in Numidia (435) before moving eastward and capturing Carthage, from where they established an independent state with a powerful navy (439). The Vandal fleet from then on formed a constant danger to Roman seafare and the coasts and islands of the Western and Central Mediterranean.
In 444 the Huns, who had been employed as Roman allies by Aetius, were united under their ambitious king Attila. When Attila turned against his former ally the Huns became a formidable threat to the empire. Attila asked for the hand of the emperor's sister Honoria with half the Western Empire's territory as his dowry. When this was refused he invaded Gaul and was only stopped with great effort by a combined Roman-Germanic force led by Aetius in the Battle of Chalons (451). The next year Attila invaded Italy and proceeded to march upon Rome, but an outbreak of disease in his army, pope Leo's plea for peace, the superstitious fear (as reported by Priscus) of the fate of Alaric (who died shortly after sacking Rome in 410), and reports of a campaign of Marcianus directed at his headquarters in Pannonia induced him to halt this campaign. Attila suddenly died a year later (453).
Aetius was slain by Valentinian, who had grown jealous of his power, in 454, and Valentinian was then himself murdered by the dead general's supporters a year later. With the end of the Theodosian dynasty, a new period of dynastic struggle ensued. The Vandals took advantage of the unrest and sailed up to Rome, which they plundered in 455.
The instability caused by usurpers throughout the Western Empire helped these tribes in their conquests, and by the 450s the Germanic tribes had become usurpers themselves. During the next twenty years, several Western emperors were installed by Constantinople, but their authority only reached as far as the barbarian commanders of the Roman troops (Ricimer (456-472), Gundobad (473-475)) allowed it to. In 475, Orestes, a former secretary of Attila, drove Emperor Julius Nepos out of Ravenna and proclaimed his own son Romulus Augustus as emperor.
In 476, Orestes refused to grant Odoacer and the Heruli federated status, prompting him to send the imperial insignia to Constantinople, installing himself as king over Italy. Although isolated pockets of Roman rule continued even after 476, the city of Rome itself was under the rule of the barbarians, and the control of Rome over the West had effectively ended. There is considered to be three rump states that continued under Roman rule in some form or another after 476, Julius Nepos controlled Dalmatia until his murder in 480, Syagrius was declared King of the Romans and ruled the Domain of Soissons until his murder in 487. Lastly, a Roman-Moor Kingdom survived in north Africa, which resisted Vandal conquest and was re-united with the Eastern Roman Empire c.533 when Belisarius reconquered North Africa.
Historical convention has determined that the Western Roman Empire ended on 4 September 476, when Odoacer deposed Romulus Augustulus. However, the issue is not clear-cut and some consider Julius Nepos, who died in 480 AD, to be the last Roman Emperor.
Julius Nepos still claimed to be Emperor of the West, ruling the rump state in Dalmatia. He was recognized as such by Byzantine Emperor Zeno and by Syagrius, who had managed to preserve Roman sovereignty in a exclave in northern Gaul, known today as the Domain of Soissons. Odoacer proclaimed himself ruler of Italy and began to negotiate with Zeno. Zeno eventually granted Odoacer patrician status as recognition of his authority and accepted him as his own viceroy of Italy. Zeno however insisted that Odoacer paid homage to Julius Nepos as the Emperor of the Western Empire. Odoacer accepted this condition and even issued coins in the name of Julius Nepos throughout Italy. This however was mainly an empty political gesture as Odoacer never returned any real power or territories to Julius Nepos. The murder of Julius Nepos in 480 prompted Odoacer to invade Dalmatia, annexing it to his Kingdom of Italy and ending the opportunity of any claims by others to the Western throne.
Following Theodoric's death in 526, the West no longer resembled the East. The West was now fully controlled by invading outside tribes, while the East had retreated and Hellenized. While the East would make some attempts to recapture the West, the Roman Empire was never the same again.
Although some eastern emperors occasionally attempted to reconquer some parts of the West, none were as successful as Justinian. The division between the two areas grew, resulting in a growing rivalry. While the Eastern Roman Empire continued after Justinian, the eastern emperors focused mainly on defending its traditional territory. The East no longer had the necessary military strength, spelling the end of any hope for reunification.
As the Western Roman Empire crumbled, the new Germanic rulers who conquered the provinces nonetheless upheld many Roman laws and traditions. Many of the invading Germanic tribes were already Christianised, though most were followers of Arianism. They quickly converted to Catholicism, gaining more loyalty from the local Roman populations, as well as the recognition and support of the powerful Roman Catholic Church. Although they initially continued to recognise indigenous tribal laws, they were more influenced by Roman Law and gradually incorporated it as well.
Roman Law, particularly the Corpus Juris Civilis collected by order of Justinian I, is the ancient basis on which the modern Civil law stands. In contrast, Common law is based on the Germanic Anglo-Saxon law.
Latin as a language never really disappeared. It combined with neighboring Germanic and Celtic languages, giving rise to many modern Romance languages such as Italian, French, Spanish, Portuguese, Romanian, Catalan, Occitan and Romansh. Latin also influenced Germanic languages such as English, German, and Dutch. It survives in its "purer" form as the language of the Roman Catholic Church (the Mass was spoken exclusively in Latin until 1969) and was used as a lingua franca between many nations. It remained the language of medicine, law, diplomacy (most treaties were written in Latin), of intellectuals and scholarship.
The Latin alphabet was expanded with the letters J, K, W and Z and is the most widely used alphabetic writing system in the world today. Roman numerals continue to be used but were mostly replaced by Arabic numerals.
The ideal of the Roman Empire as a mighty Christian Empire with a single ruler continued to seduce many powerful rulers. Charlemagne, King of the Franks and Lombards, was even crowned as Roman Emperor by Pope Leo III in 800. Emperors of the Holy Roman Empire like Otto I, Frederick I Barbarossa, Frederick II, and Charles V, French King Louis XIV, as well as French Emperor Napoleon I, among others, tried to a certain extent to resurrect it, but none of their attempts were ultimately successful.
A very visible legacy of the Western Roman Empire is the Roman Catholic Church. The Church slowly began to replace Roman institutions in the West, even helping to negotiate the safety of Rome during the late 5th century. As Rome was invaded by Germanic tribes, many assimilated, and by the middle of the medieval period (c.9th and 10th centuries) the central, western and northern parts of Europe had been largely converted to the Roman Catholic Church and acknowledged the Pope as the Vicar of Christ.