through the whole country. Besides the forts along the east and south coasts, and the system of galleys based upon them, a host of new precautions becomes evident. The walls of London were furnished with bastion towers, the stones for which were taken from dwelling-houses, now no longer required by a dwindling town-population. Here and there the broad Roman gateways of townships were narrowed to half their size with masonry, a lasting proof of the increasing insecurity of the times. All over the country hoards of coins have been found, hardly any of which are later than the year A.D. 400. Over this fertile, peaceful, ordered world lay the apprehension of constant peril.
Like other systems in decay, the Roman Empire continued to function for several generations after its vitality was sapped. For nearly a hundred years our Island was one of the scenes of conflict between a dying civilisation and lusty, famishing barbarism. Up to the year 300 Hadrian’s Wall, with its garrisons, barred out the Northern savages, but thereafter a new front must be added. At the side of the “Duke of the Northern Marches” there must stand the “Count of the Saxon Shore.” All round the eastern and southern coasts, from the Wash to Southampton Water, a line of large fortresses was laboriously built. Eight have been examined. Of these the chief was Richborough, known to the generation of the First World War as an invaluable ferry-port for the supply of the armies in France.
There is some dispute about the strategic conceptions upon which these strongholds were called into being. Many disparaging judgments have been passed upon a policy which is accused of seeking to protect four hundred miles of coastline from these eight points. Obviously these strictures are unjust. The new line of coastal fortresses could only have had any value or reason as bases for a British-Roman fleet. Such a fleet, the Classis Britannica, had been maintained from the first century. Tiles with an Admiralty mark show that it had permanent stations at Dover and Lympne. But the whole coast was organised for defence, and for long periods these measures proved effective. Vegetius, writing in the fourth century on the art of war, mentions a special kind of light galley attached to the British fleet. These vessels, the hulls, sails, the men’s clothes, and even faces, were painted sea-green, to make them invisible, and Vegetius tells us that in naval parlance they were called “the Painted Ones.” As the Imperial and British sea-power gradually became unequal to the raiders the ramparts of the fortresses grew higher and their usefulness less. Flotilla defence by oared galleys working from bases fifty to a hundred miles apart could not contend indefinitely with raiding thrusts. Even a High Sea Fleet capable of keeping the sea for months at a time off the coasts of what are now called Holland, Germany, and Denmark, though a powerful deterrent, would have been too slow to deal with oared boats in calm weather.
The Roman Britons were lively and audacious members of the Empire. They took a particularist view, yet wished to have a hand in the game themselves. As time passed the Roman garrison in Britain steadily became more British, and towards the end of the third century it assumed a strong national character. While glorying in the name of citizens and Romans, and having no desire for independence, both province and army adopted a highly critical attitude towards the Imperial Government. Emperors who disregarded British opinion, or sacrificed British interests, above all those who could be accused of neglecting the defences of the province, were the objects of active resentment. A series of mutinies and revolts aggravated the growing dangers of the times. No one can suppose that the Roman military centres at Chester, York, or Caerleon-on-Usk threw up claimants for the Imperial diadem unsupported by a strong backing in local opinion. These were not merely mutinies of discontented soldiers. They were bold bids for control of the Roman Empire by legions only a few thousand strong, but expressing the mood, sentiments, and ambitions of the society in which they lived. They left the local scene for the supreme theatre, like players who wish to quit the provinces for the capital. Unhappily they took away with them at each stage important elements of the exiguous military forces needed to man the dykes.  The Emperor Diocletian has gone down to history principally as the persecutor of the early Christians, and the enormous work which he achieved in restoring the frontiers of the ancient world has remained under that shadow. His policy was to construct a composite Cæsarship. There were to be two Emperors and two Caesars, he himself being the senior of the four. In due course the Emperors would retire in favour of the Cæsars, new ones would be appointed, and thus the succession would be preserved. The co-Emperor Maximian, sent to Gaul in 285, and responsible for Britannia, was deeply concerned by the raiding of the Saxon pirates. He strengthened the Channel fleet, and put at its head a sea officer from the Low Countries named Carausius. This man was tough, resolute, ambitious, and without scruple; from his base at Boulogne he encouraged the raiders to come and pillage, and then when they were laden with plunder he fell upon them with Roman-British flotillas, captured them by scores, and destroyed them without mercy. His success did not satisfy the British community; they accused him of having been in league with those he had destroyed. He explained that this was all part of his ambush; but the fact that he had retained all the spoil in his own hands told heavily against him. Maximian sought to bring him to execution, but Carausius, landing in Britain, declared himself Emperor, gained the Island garrison to his cause, and defeated Maximian in a sea battle. On this it was thought expedient to come to terms with the stubborn rebel, and in the year 287 Carausius was recognised as one of the Augusti in command of Britain and of Northern Gaul.
For six years this adventurer, possessing sea-power, reigned in our Island. He seems to have served its interests passably well. However, the Emperor Diocletian and his colleagues were only biding their time, and in the year 293 they cast away all pretence of friendship. One of the new Cæsars, Constantius Chlorus, besieged and took Boulogne, the principal Continental base of Carausius, who was soon assassinated by one of his officers. The new competitor sought to become Emperor in his stead. He did not gain the support of the British nation and the whole country fell into confusion. The Picts were not slow to seize their advantage. The Wall was pierced, and fire and sword wasted the Northern districts. Chlorus crossed the Channel as a deliverer. His colleague, with part of the force, landed near Portsmouth; he himself sailed up the Thames, and was received by London with gratitude and submission. He restored order. A gold medallion discovered at Arras in 1922 reveals him at the head of a fleet which had sailed up the Thames. He drove back the Northern invaders, and set to work to restore and improve the whole system of defence.
Continuous efforts were made by the Roman-British community to repel the inroads, and for two or three generations there were counter-strokes by flotillas of galleys, and hurried marchings of cohorts and of British auxiliaries towards the various thrusts of raid or invasion. But although the process of wearing down was spread over many years, and misery deepened by inches, we must recognise in the year 367 circumstances of supreme and murderous horror. In that fatal year the Picts, the Scots, and the Saxons seemed to work in combination. All fell together upon Britannia. The Imperial troops resisted manfully. The Duke of the Northern Marches and the Count of the Saxon Shore were killed in the battles. A wide open breach was made in the defences, and murderous hordes poured in upon the fine world of country houses and homesteads. Everywhere they were blotted out. The ruins tell the tale. The splendid Mildenhall silver dinner service, now in the British Museum, is thought to have been buried at this time by its owners, when their villa was surprised by raiders. Evidently they did not live to dig it up again. The villa life of Britain only feebly recovered from the disaster. The towns were already declining. Now people took refuge in them. At least they had walls.
The pages of history reveal the repeated efforts made by the Imperial Government to protect Britannia. Again and again, in spite of revolts and ingratitude, officers and troops were sent to restore order or drive back the barbarians. After the disasters of 367 the Emperor Valentinian sent a general, Theodosius, with a considerable force to relieve the province. Theodosius achieved his task, and once again we find on the coastal fortifications the traces of a further strong reconstruction. Untaught however by continuing danger, the garrison and inhabitants of Britain in 383 yielded themselves willingly to a Spaniard, Magnus Maximus, who held the command in Britain and now declared himself Emperor. Scraping together all the troops he could find, and stripping the Wall and the fortresses of their already scanty defenders, Maximus hastened to Gaul, and defeated the Emperor Gratian near Paris. Gratian was murdered at Lyons by his troops, and Maximus became master of Gaul and Spain as well as Britain. For five years he struggled to defend his claim to these great dominions, but Theodosius, who had succeeded Gratian, at length defeated and slew him.