Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
Now Britain had never been visited by the Romans, and was entirely unknown to them before the time of Caius Julius Caesar, who, in the year 693 after the foundation of Rome, but the sixtieth year before the Incarnation of our Lord, was consul with Lucius Bibulus. While he was making war upon the Germans and the Gauls, who were divided only by the river Rhine, he came into the province of the Morini, whence is the nearest and shortest passage into Britain. Here, having provided about eighty ships of burden and fast-sailing vessels, he sailed over into Britain; where, being first roughly handled in a battle, and then caught in a storm, he lost a considerable part of his fleet, no small number of foot-soldiers, and almost all his cavalry. Returning into Gaul, he put his legions into winter-quarters, and gave orders for building six hundred sail of both sorts. With these he again crossed over early in spring into Britain, but, whilst he was marching with the army against the enemy, the ships, riding at anchor, were caught in a storm and either dashed one against another, or driven upon the sands and wrecked. Forty of them were lost, the rest were, with much difficulty, repaired. Caesar’s cavalry was, at the first encounter, defeated by the Britons, and there Labienus, the tribune, was slain. In the second engagement, with great hazard to his men, he defeated the Britons and put them to flight. Thence he proceeded to the river Thames, where a great multitude of the enemy had posted themselves on the farther side of the river, under the command of Cassobellaunus, and fenced the bank of the river and almost all the ford under water with sharp stakes: the remains of these are to be seen to this day, apparently about the thickness of a man’s thigh, cased with lead, and fixed immovably in the bottom of the river. This being perceived and avoided by the Romans, the barbarians, not able to stand the charge of the legions, hid themselves in the woods, whence they grievously harassed the Romans with repeated sallies. In the meantime, the strong state of the Trinovantes, with their commander Androgius, surrendered to Caesar, giving him forty hostages. Many other cities, following their example, made a treaty with the Romans. Guided by them, Caesar at length, after severe fighting, took the town of Cassobellaunus, situated between two marshes, fortified by sheltering woods, and plentifully furnished with all necessaries. After this, Caesar returned from Britain into Gaul, but he had no sooner put his legions into winter quarters, than he was suddenly beset and distracted with wars and sudden risings on every side.