How did Caesar's conquest of Gaul change both Rome and Gaul?
Julius Cesar is one of the most famous men in history. He was one of the greatest military commanders of all time and transformed the Roman Republic into an Empire. One of Cesar’s greatest achievements was Gaul's conquest in a series of bloody wars (57-51 BCE). This conquest was not only a remarkable achievement, but it had a profound impact on the future of Europe. It changed the balance of power within the Roman Republic.
Ultimately, Caesar overthrew the Roman Republic and established the Imperial system under his grand-nephew Octavian (Augustus). The Romanization of the Gallic provinces led to the development of Gallo-Roman culture and the end of Celtic Gaul. One of the long-term consequences of the Caesarean conquest of Gaul was that it probably saved Celtic Gaul from becoming overrun by German tribes. The conquest of Gaul confirmed that Rome was not just a Mediterranean power but a European one. After the conquest, Rome was free to take over other areas in western Europe, including Britain.
How did Julius Caesar conquer Gaul?
Julius Caesar was an aristocrat and a prominent politician in Rome. He had entered an informal arrangement with Pompey and Crassus, which had brought a measure of stability in Rome after many years of conflict. Cesar had himself appointed as commander of Roman Legions in the south of Gaul. Gaul was an area that approximated modern France, Luxembourg, part of the Netherlands, and Belgium. Gaul covered much of Western Europe. Much of the area was dominated by Celtic tribes who had developed a sophisticated political system and culture. Cesar and some legions were in the south of Gaul to protect the Greek city-state of Massalia (Marseilles) from attack by Celtic tribes. Cesar was only instructed to repel any attackers, but as he was in the area, the Helvetti, from modern Switzerland, migrated into the region around Massalia.
Caesar portrayed this to the Roman Senate as an invasion and attacked the Helvetti. Ultimately, Caesar drove the Helvetti back to their homeland. He then used the threat posed to some allied Gallic tribes from the Germans to justify intervention in Gaul. Caesar did not have the permission of the Senate to invade Gaul and to annex it. Indeed, the Gallic wars were started by Caesar on his initiative. He wanted military glory and booty to further his political career and to pay off his many debts. Gaul now was divided among a series of tribal confederacies, even though they all considered themselves Celts.
Caesar skillfully exploited the divisions between the tribes to his advantage. Many of the Celtic tribes became his allies, such as the Aedui.  These allies were allowed a measure of self-rule. It seemed likely that they did not fully understand the extent of Roman ambitions in Gaul. They may have believed that Caesar would eventually leave the region. However, Caesar and the Romans were in Gaul to stay. One by one, Caesar, throughout five years, would conquer the tribes, or they became his allies.
Caesar was a brilliant propagandist, and he had his dispatches from his campaigns read publicly in Rome. There were later collected together to form the history ‘The Gallic Wars.’ Because of the war, Caesar became very rich and famous, and soon he even began to eclipse Pompey the Great. Caesar could defeat war-like tribes such as the Nervii and Belgae because of his superior tactics and legions' brilliance. On many occasions, he conquered significantly larger Celtic armies. The Roman general cleverly exploited Celtic battle tactics for his advantage and used fixed projectile firing weapons such as the scorpion and the ballista to break up the Gauls' mass charges.
By 54 BC, most of Gaul was under Roman control. However, there was widespread discontent. According to Plutarch, the Celtic pagan priesthood known as the druids began to ‘incite the Celtic aristocracy against the Romans.’ Secretly, the Gauls united and allied to expel the Romans. Vercingetorix, chief of the Arverni tribe, led the many Gallic tribes and states. He proved to be a formidable general. He and his army drove the Romans from many areas. They adopted guerrilla tactics and usually refused to engage the Roman legions in battle. 
When Caesar was besieging the Gauls at Alesia, Vercingetorix surrounded the Roman legions in a brilliant maneuver. The Roman army would have been demolished under any other general, but Caesar successfully turned that tide and defeated the Gaul’s at Alessia. The Battle of Alesia ended the Gallic rebellion. Vercingetorix was later strangled as part of the Triumph of Caesar in Rome. After his victories, Caesar typically left the local Gaul elites in power and imposed no new burdens on them. These favorable terms allowed Rome to keep Gaul (already exhausted by so many unsuccessful battles) in obedience. Caesar’s victory in Gaul was total, and there was no further attempt by the Gauls to throw off Roman rule. The area became a crucial part of the Roman Empire until the fall of the Western Empire in the mid-5th century AD.
How did the Conquest of Gaul strengthen Caesar's Political standing?
The first and most immediate consequence of the war was that it upset Rome's balance of power. The First Triumvirate was a political arrangement between Pompey, Crassus, and Cesar. This arrangement allowed the three most powerful men in Rome to achieve their respective goals. However, Crassus was killed in an ill-advised invasion of Parthia. This left Pompey and Cesar as the two most powerful men in Rome.
Pompey and Caesar were not only leaders of the Triumvirate but family. Pompey had been the son-in-law of Caesar. Both Julia, Caesar's daughter, and Pompey’s wife, died in childbirth. Her death weakened the alliance between the two men. Many regarded Cesar as a war-monger in the Roman Senate and believed that he was engaged in Gaul's illegal war. The Roman senators were not concerned with the Gauls' fate but were extremely suspicious of Caesar's motives. They believed that he was building up a power base in Gaul, and he was treating the legions under his command as his private army.
The senators feared that Cesar would seize power and become a dictator just as Sulla had. Many of the Roman elite were suspicious of Cesar because of Marius's close connections and the Populares party. During the war, Caesar had retained control of his legions because he claimed that they were needed in Gaul's conquest. With the end of the conflict, he was not supposed to retain control of his army.
After Cesar’s great victory at Alessia, the Senate demanded that he return to Rome and command his legions. The Senate had the law on its side, but Caesar was worried that he would be vulnerable to his Roman enemies if he gave up his legions. Caesar demanded that he be given an extraordinary command and that he be allowed to command some legions. Pompey sided with the Senate, and he began to regard Cesar as his enemy.
The Senate rejected Caesar's proposal. Caesar, bold as ever, tried to force the issue and marched his legions on Rome. Caesar claimed that there was a conspiracy against him ‘it was evident to everyone that war was designed against Caesar.’  When he ordered his legionnaires to cross the River Rubicon, he defied the Senate, which made the Civil War inevitable. The Gallic Wars made Cesar the most powerful man in Rome, resulting in a civil war. Caesar used his legions of battle-hardened veterans to defeat Pompey and the Republican army at Pharsalus. This civil war led to Caesar's ascent as Rome's sole power. Caesar’s Gallic Wars were an important stage in the final downfall of the Roman Republic.
How did the Conquest change Gaul?
Caesar destroyed the Celtic civilization in Gaul. The Celtic priesthood, the druids, were key to the culture and religion of Gaul. The Gauls, despite their sophistication, were a pre-literate people, although some used Greek for official purposes. The Druids were renowned for their remarkable memories, and they retained the oral history of the Gauls. The druids were also the judicial class, and they alone could remember the legal codes of the various tribes. The priestly class also played a significant role in the Celts' oral literature.
The druids were among the Romans' fiercest opponents, and Caesar recognized them as one of Rome's primary obstacles. The Romans also hated the druids because they allegedly practiced human sacrifice as part of their religion. Caesar targeted the druids during his war with the Gallic tribes. In his history of the Gallic Wars, he reported that his armies would often target the Druids' sacred groves and killed many of these priests. He justified this violence because he argued that they were barbarians who engaged in bloody rites and ceremonies. Caesar eliminated the druids and destroyed their shrines and sanctuaries.
As the druids disappeared, the Celtic religion and culture rapidly decline. Trade between Gaul and Rome increased, and the Romans imposed their laws on Gauls. The increased trade transformed the province, and it quickly Romanized. The old Gallic elite soon began to imitate the Romans, and many learned Latin. Soon Roman-style villas dotted the Gaulish landscape. By the first century AD, the Gallic elite was so Romanized that some were admitted into the Senate by Emperor Claudius.. Many historians believe that Celtic Gaul was doomed anyway and that the German tribes would have conquered it. Around the time of the Roman invasion, many German tribes were raiding and even settling in Gaul. Caesar's justifications for his war were that he sought to protect Roman interests in Gaul from the Germans.
How did the Conquest of Gaul change Rome?
By conquering Gaul, Caesar greatly expanded the influence of Rome in Western Europe. Before this conquest, the Roman Republic had been centered on the Mediterranean. Caesar transformed Rome into a European power. Suddenly Rome’s influence was no longer centered on the Mediterranean, which had important consequences for its future expansion. Even before the Gallic campaign was over, Rome turned its attention to other western and central European areas. Caesar raided Britain in 55 BC and crossed the Rhine, and fought a war with the powerful Suebi tribe a year later.
Roman Emperors followed the example of Caesar and tried to expand their Empire in Europe. Emperor Augustus invaded Germania and conquered most of the area, right up to the River Elbe. However, this resulted in a great rebellion and the loss of three legions in the Teutoburg Forest. This defeat led to Augustus setting the border with Germania at the Rhine. He did manage to retain the Rhineland for the Roman Empire. Claudius had better luck. He successfully conquered most of Britain apart from Scotland in the First Century AD. The future expansion of the Roman Empire would not have been possible without the conquest of Gaul. Caesar inspired future leaders to try and conquer more land in western Europe. The great Roman historian Tacitus related how Claudius, over 100 years later, felt duty-bound to invade further into Britain and complete Caesar's work.
The conquest of Gaul by Caesar was to have momentous consequences. It resulted in a large area of western Europe coming under the sway of the Romans. From Gaul, they could expand their empire into parts of Germany and Britain. The Roman province of Gaul was to remain part of the Roman Empire until 450 AD. Roman's conquest changed Gaul's character and led to the decline of the local Celtic civilization and the rise of a Romano-Gallic culture. This culture played a critical role in the development of the kingdom of France during the Middle Ages. If Caesar had not conquered, the Germanic tribes might have completely overrun Gaul.
Perhaps the most immediate consequence of Gaul's conquest was that it upset the balance of power in Rome. It led to a confrontation between Cesar and the Roman Senate over control of Gaul's legions, which led to a civil war. Over the long term, this resulted in Caesar's heir becoming the first Emperor of Rome. It could be argued that the most dramatic consequence of the Roman victories in Gaul was that they ultimately led to the emergence of the Imperial system in Rome.
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