He continued north of the Alps each summer and he would leave his army there in garrison each winter while he came south to conduct the civil administration of Cisalpine Gaul and Illyricum and to keep in contact with Rome. Caesar became determined to conquer and make a province of the whole of Gaul. After his defeat of the Belgic tribes in the north and the submission of the maritime tribes on the Atlantic seaboard, he believed that the task had all but been accomplished. Caesar decided to make two short reconnaissance expeditions, one across the Rhine. and the other across the Straits of Dover to Britain. In a longer and more serious invasion of Britain he crossed the Thames and received the submission of the supreme commander of the southeastern Britons, Cassivellaunus. Caesar had avoided recall to Rome at the end of the five years of command voted to him by coming to a fresh agreement with Pompey and Crassus at Luca. The optimates in control of the senate, now awake to the immense increase in Caesar’s personal power, wealth, and prestige, kept Pompey in Italy, allowing him to govern his Spanish provinces by deputies. Pompey’s own attachment to Caesar was broken when Caesar’s daughter Julia to whom Pompey had been happily married since 59 BC died in 54 BC Crassus was killed by the Parthians at Carrhae in Mesopotamia. In planning Caesar’s return to civil life in Rome he could assume that as soon as he lost the immunity from prosecution which his military command conferred, his political enemies would endeavor to secure his exile by prosecuting him in the courts either for bribery or for the use of force in politics. In Rome there was support in the senate for a negotiated compromise when Curio put forth the proposal by which Caesar would give up his military command and stand in person at the consular election on condition that Pompey abandon his military command at the same time. On January 7, 49 BC Antony and one of his fellow tribunes were warned that their lives would be in danger if they sustained their veto and the proclamation of military law was passed. Caesar was told to leave his troops behind and cross the Rubicon into Rome alone. Caesar knew that this was a death sentence for him so he did not leave his troops but marched into the city and caused a civil war. He defeated Pompey’s troops in many battles and became the dictator of Rome.
From the time that he had first faced battle in Gaul and discovered his own military genius, Caesar was evidently fascinated and obsessed by military and imperial problems. He gave them an absolute priority over the more delicate by no less fundamental task of revising the Roman constitution.