For the invasion Claudius concentrated four legions, with auxiliaries and cavalry, in Gaul. This meant 24,000 legionaries, supposing the cohorts to be at full strength, with, as is probable, as many auxiliaries. Taking the cavalry into consideration, and making a deduction of 20 per cent. for absentees, we can hardly reckon the force at less than 40,000 effectives; it may have been even stronger. The commander was Aulus Plautius, a veteran who had grown grey in war, and who, to judge from his record, was singularly fitted for his post. Claudius himself was on the way from Rome to join his army with the Prætorian Guard.

For all practical purposes the Roman army was still the army of Marius and Cæsar, but the proportion of auxiliaries and cavalry was much greater. Of the legions three came from the Army of the Rhine: II., ‘Augusta’; XIV., ‘Gemina Martia’; and XX., ‘Valeria Victrix.’ From the Army of Pannonia, or the Upper Danube, came Legio IX., ‘Hispana.’ The XIVth was to win the proud title of ‘Conqueror of Britain’ during its stay of twenty-five years. ‘Valeria Victrix’ remained for more than three centuries, and the IInd did not leave until 407.

The legions had now become so fixed in their frontier cantonments that to move them bodily to other regions was a delicate business. The new Army of Britain grumbled, and seemed about to mutiny. Its temper was not improved by the fact that the Imperial commissioner appointed to inquire into their grievances was the Emperor's treasurer, Narcissus, a Greek civilian! One can almost hear the Roman ‘Tommies’ asking, with much profanity, why their dignity should be thus insulted, and they expressed their contempt for the unmentionable civilian by a riotous demonstration. The old General, however, whom they respected, soon recalled them to their duty. The affair had important results, for the British kings were induced by the news to believe that the expedition would not sail, and so were unprepared when it suddenly appeared in Kent.

The landing-place this time was probably Rutupiæ (Richborough, near Sandwich), which for some centuries to come was to be the usual starting-point for the Continent. The men of Kent were too unprepared to attempt to oppose the landing, but they harassed the flanks of the army as it marched for the Thames along the old, old track that Cæsar had traversed a century before. This time the British guerrilla tactics had slight effect; there was ample cavalry to feel ahead, and ample light infantry to guard the flanks. We hear no more of the stunning and disordering surges of chariotry among the Roman battalions—indeed, there is some reason to believe that, with the introduction and breeding of larger horses fit for riding, it was already in a state of decline.

Meanwhile Togodubn and Caradoc had crossed the Thames, and were prepared to oppose the Roman advance at the Medway, probably near Rochester. The position was a strong one, with the broad river and expanses of mud flat and marsh in its front. Plautius, however, forced the passage by a wide turning movement up the river under his able legatus, T. Flavius Vespasianus, while a large body of Batavian and North Gallic auxiliaries, accustomed to amphibious operations, with the greatest daring swam the river on the right. The Britons were thus forced to abandon the river-bank, but they fell back on the high ground towards Cobham and Shorne and stood firm. Next day a great battle was fought. The Britons made a fine resistance, and nearly captured the legatus Hosidius Geta; but were at last defeated, and retreated to the Thames. One could wish that we had some better authority than Dion Cassius, who wrote more than a hundred and fifty years later, and is so confused and rhetorical that we read him with deep distrust. We long for even the unmilitary and epigrammatic Tacitus, but his books relating to the early years of Claudius are lost.

Dion says, in brief, that the Britons crossed the Thames near where it enters the sea. They did so easily ‘because they knew the firm ground ... and the easy passages, ... but the Romans following them came to grief at this spot.’ We can hardly imagine the Thames as fordable anywhere below London, and the probable meaning of the passage is that the Britons traversed the marshes by well-known tracks, and then crossed the river in boats or on rafts.

Now comes the most curious part; and, if Dion could be relied upon, we have an invaluable reference to the earliest London Bridge. The Celts, he says, again swam the river, and other troops forced a bridge a little way upstream. We can hardly imagine a bridge existing below London, and if it stood anywhere, it would certainly be at the one place clearly marked out by Nature for the passage across the river of the road from the south-east to Verulam. London was such a remarkable road centre in Roman times that we cannot easily believe that it was not so long before, and the construction of a pile bridge was certainly not beyond the resources of a powerful ruler like Cunobelin, who had, without any doubt, skilled foreigners at his disposal, besides abundance of unskilled labour. Moreover, it explains satisfactorily the importance of London, which Tacitus describes as a great trading centre only eighteen years later.

Whatever his authorities, Dion’s account of the operations, studied with the aid of the map, is logical and clear. The Britons are driven back from the Medway, and retreat to the estuary of the Thames across dangerous marshes—that is, we can hardly doubt that Vespasian’s turning movement cut their line of retreat on London, and they were forced to fall back northward by Higham into Cliffe Marshes. The Roman pursuit was checked by the difficulties of the ground, but Plautius was between the Britons and London. He therefore marched for the bridge. The Britons, hurrying from Tilbury Marshes, reached London too late to destroy the bridge or occupy it with more than a fraction of their forces, if indeed at all. The bold action of the Batavians, who accomplished a more difficult feat than the swimming of the Medway, coupled with the seizure of the bridge, forced the Britons to abandon the defence of the Thames.

Togodubn had been slain in the course of the campaign, but Caradoc was alive and undismayed. He retreated towards Camulodunum, not upon his ancestral capital of Verulam. Clearly, Camulodunum was of greater importance. Meanwhile Claudius had landed with the Imperial Guards and was coming up. Dion says that the fighting had been so fierce that the reinforcements which he brought were very necessary. This may be a flight of rhetoric, but it is evident that the resistance was stubborn. Having effected a junction with his general, Claudius advanced on Camulodunum. Caradoc stood to fight somewhere on the road—perhaps at the Blackwater—and was defeated finally and utterly. Camulodunum was taken, the empire broke up or submitted, and the king, with his family and a remnant of his army, fled away across Britain into the country of the Silures (South Wales). Claudius himself only waited to enter Camulodunum and to declare it the capital of the Roman Province of Britannia, and then returned to Gaul.

The heart of the Catuvellaunian dominion was now occupied with little difficulty. The Iceni and Regni sent in their submission; but Caradoc with the Silures was preparing for a last desperate stand for freedom, if not for empire; and the Belgæ and Durotriges made a gallant resistance to Vespasian, who marched against them with Legio II. Thirteen fierce engagements were necessary before the conquest was complete, and Vespasian on one occasion owed his life to his son Titus, the future destroyer of Jerusalem. But his work was very thoroughly done, and within six years Roman rule was firmly established as far as the Exe. The wild Damnonii beyond that river were left now and afterwards very much to themselves. No doubt they made submission, but the great western road never went beyond Isca Damnoniorum (Exeter). The tin trade of Cornwall seems to have languished during the Early and Middle Empire; but when in the third century the mines once more began to disgorge their treasures, the ingots were carried to the sea on the backs of pack-animals. Until the eighteenth century pack-trains with correspondingly narrow tracks were the rule in Devon and Cornwall. The famous bridge of Bideford was scarcely more than wide enough to admit of the passage of a loaded horse.