于是，他率军渡过分隔阿尔卑斯高卢行省和意大利的鲁比康河，向罗马挺进。所过之处，老百姓将他当作"人民之友"来热烈欢迎。他一举攻人罗马，庞培被迫逃到希腊。悄撒率军追击，在法尔萨拉附近击败庞培及其追随者。庞培渡过地中海，逃往埃及。当他登陆后，年轻的埃及国王托勒密命人暗杀了他。几天后，恺撒也抵达埃及，随即发现自己落入了一个阴谋的陷阱。埃及人和仍忠于庞培的罗马驻军联合向他发动攻击。

　　Fortune was with Caesar. He succeeded in setting fire to the Egyptian fleet. Incidentally the sparks of the burning vessels fell on the roof of the famous library of Alexandria (which was just off the water front,) and destroyed it. Next he attacked the Egyptian army, drove the soldiers into the Nile, drowned Ptolemy, and established a new government under Cleopatra, the sister of the late king. Just then word reached him that Pharnaces, the son and heir of Mithridates, had gone on the war-path. Caesar marched northward, defeated Pharnaces in a war which lasted five days, sent word of his victory to Rome in the famous sentence "veni, vidi, vici," which is Latin for "I came, I saw, I conquered," and returned to Egypt where he fell desperately in love with Cleopatra, who followed him to Rome when he returned to take charge of the government, in the year 46.

　　不过。恺撒很走运。他成功地焚毁了埃及舰队。可不巧的是，大火迸出的火星落在埃及著名的亚历山大图书馆的屋顶上（它正好位于码头边），将这座珍藏着无数古代典籍的建筑付之一炬。摧毁埃及海军后，恺撒回过头来进攻埃及陆军，将惊慌溃逃的士兵赶进尼罗河，托勒密本人也溺水身亡，随即建立了一个以已故国王的姐姐克娄帕特拉为首的新政府。此时又有消息传来，米特拉达特斯的儿子兼继承人法那西斯准备发动战争，为自杀的父亲复仇。恺撒立刻挥师北上，持续作战五昼夜，打败了法那西斯。在给元老院的捷报中，他为世人留下了一句名言，"veni，vidi，vici"，意思是"我来了，我看见了，我征服了！"然后恺撒返回埃及，不可救药地坠入情网，拜倒在女王克娄帕特拉魅力非凡的裙下。公元46年，恺撒携克娄帕特拉一起返回罗马，接掌政权。