Gaius Julius Caesar (July 102 BC or 100 BC – 15 March 44 BC), was a Roman military and political leader and one of the most influential men in history. He played a critical role in the transformation of the Roman Republic into the Roman Empire. Caesar's victories in the conquest of Gaul, completed by 51 BC, extended Rome's territory to the English Channel and the Rhine. Caesar became the first Roman general to cross both when he built a bridge across the Rhine and conducted the first invasion of Britain. He wrote an account of his campaigns in The Gallic War.
These achievements granted him unmatched military power and threatened to eclipse the standing of Pompey, who had realigned himself with the Senate after the death of Crassus in 53 BC. With the Gallic Wars concluded, the Senate ordered Caesar to step down from his military command and return to Rome. Caesar refused the order, and instead marked his defiance in 49 BC by crossing the Rubicon River with a legion, leaving his province and illegally entering Roman Italy under arms. Civil war resulted, and Caesar's victory in the war put him in an unrivaled position of power and influence.
After assuming control of government, Caesar began a program of social and governmental reforms, including the creation of the Julian Calendar. He centralized the bureaucracy of the Republic and was eventually proclaimed "dictator in perpetuity", giving him additional authority. But the underlying political conflicts had not been resolved, and on the Ides of March (15 March) 44 BC, Caesar was assassinated by a group of rebellious senators. A new series of civil wars broke out, and the constitutional government of the Republic was never fully restored. Caesar's grandnephew and adopted heir, Augustus Caesar, became the first Emperor after defeating his opponents.
Augustus referenced his great-uncle Julius Caesar's successful conquest of Gaul as the Roman Empire began making its final, ultimately unsuccessful drive, to conquer Germany. Conversely, Arminius was also aware of the conquest of Gaul, and the fact that the Gauls themselves had grown more "Romanized" since Caesar's arrival, a fate he wanted to prevent for his people.
Augustus had also learned from his adopted father's assassination, and carefully maintained a public pretense that he shared power with Roman Senate, whereas Caesar senior could not.