Caesar's first trip into Britain was less an invasion than an expedition. He took only two legions; his cavalry auxiliaries were unable to make the crossing despite several attempts. Caesar crossed late in the season, and in great haste, leaving well after midnight on 23 August. Initially, he planned to land somewhere in Kent, but the Britons were waiting for him. He moved up the coast and landed—modern archeological finds suggest at Pegwell Bay—but the Britons had kept pace and fielded an impressive force, including cavalry and chariots. The legions were hesitant to go ashore. Eventually, the X legion's standard bearer jumped into the sea and waded to shore. To have the legion's standard fall in combat was the greatest humiliation, and the men disembarked to protect the standard bearer. After some delay, a battle line was finally formed, and the Britons withdrew. Because the Roman cavalry had not made the crossing, Caesar could not chase down the Britons. The Romans' luck did not improve, and a Roman foraging party was ambushed. The Britons took this as a sign of Roman weakness and amassed a large force to assault them. A short battle ensued, though Caesar provides no details beyond indicating the Romans prevailed. Again, the lack of cavalry to chase down the fleeing Britons prevented a decisive victory. The campaigning season was now nearly over, and the legions were in no condition to winter on the coast of Kent. Caesar withdrew back across the Channel.

Gilliver notes that Caesar once again narrowly escaped disaster. Taking an understrength army with few provisions to a far-off land was a poor tactical decision, which easily could have led to Caesar's defeat – yet he survived. While he had achieved no significant gains in Britain, he had accomplished a monumental feat simply by landing there. It was a fabulous propaganda victory as well, which was chronicled in Caesar's ongoing Commentarii de Bello Gallico. The writings in the Commentarii fed Rome a steady update of Caesar's exploits (with his own personal spin on events). Caesar's goal of prestige and publicity succeeded enormously: upon his return to Rome, he was hailed as a hero and given an unprecedented 20-day thanksgiving. He now began planning for a proper invasion of Britain.