It was, as we have seen, in the year 296 that Britain was recovered for the empire by Constantius. Ten years afterwards that emperor, in failing health and knowing that he had not long to live, was looking anxiously eastwards for the arrival of his favourite son, the offspring of his concubine Helena, the brave and brilliant soldier Constantine. Diocletian and Maximian had both abdicated the empire. Constantius Chlorus was now raised from the rank of Cæsar to the higher rank of Augustus, but he shared that dignity with a jealous colleague, Galerius, who had been allowed to name the two new Cæsars. Of those two junior partners Constantine was not one. Worse than that, he was retained as a kind of hostage at the Bithynian palace of Galerius, and it was doubtful whether father and son would ever be allowed to meet again. But in a moment of irresolution or of alarm Galerius gave the desired permission, and Constantine, not risking the chance of its withdrawal, departed from the court without formal leave-taking and hurried across Europe to Boulogne where his father was then residing. It was currently reported two centuries later that in order to prevent the possibility of pursuit he ordered the post-horses at each imperial mutatio, which he did not himself require, to be either killed or so mutilated as to make them unfit for travel. Gibbon derides this “very foolish story,” but it is not easy to understand why, if untrue, it should have obtained such general acceptance.
However this may be, it is certain that Constantine arrived safely at his father’s headquarters at Boulogne, shared with him the labours of a short campaign against the Picts, and was present in his chamber, in the Prætorian palace at Eburacum, when, worn out with toil and disease, Constantius Chlorus breathed his last (July 25, 306). His own elevation to the imperial dignity by the soldiers, who enthusiastically hailed him as Augustus, followed immediately after, and we may fairly suppose that the same place which had witnessed the death of the father witnessed also the accession of the son. He speedily quitted Britain in order to take part in that desperate game of empire, with partners constantly changing and occasionally putting one another to death, from which after eighteen years he finally arose sole emperor. With all this later life of his, with his adoption of Christianity, with his choice of a new capital by the Bosphorus, with his convocation of the Nicene council, we have here no concern; but it is worth while to emphasise the fact that a reign so immensely important for all the after-history of Europe and of the world began in our island by the slow, wide-wandering river Ouse. Thus in a certain sense York is the mother-city of Constantinople.
We come now to another blank half century in the history of Roman Britain. Save for an obscure hint of the presence of the Emperor Constans, son of Constantine, at some time between 337 and 350, we have scarcely any information as to British affairs from the proclamation of Constantine in 306 to the despatch of the elder Theodosius to Britain in 367. This general, father of the more celebrated emperor of the same name, was sent by the Emperor Valentinian to restore some degree of order in the unhappy island, which had suffered from rapacious governors, from accusations of disloyalty cruelly avenged, and more recently from bloody inroads of the Picts and Scots with whom were now joined a tribe who are called “the most valiant nation of the Attacotti,” but who, if we may believe the extraordinary statement of St. Jerome, were actually addicted to the practice of cannibalism. In the three years of Theodosius’ command, the northern invaders were driven back to their mountains, the inhabitants of “that ancient town which was formerly called Londinium but which (in the fourth century) “more often bore the name Augusta” were relieved from their terrors: a new province, the geographical position of which is not made known to us, was staked out and received the name Valentia, in compliment to the emperor. For the time, but probably not for a long time, the blessings of “the Roman peace” were restored to Britain. The general who had achieved this result was shortly after executed at Carthage, a victim to the cowardly suspicion and jealousy of the Emperor Valens, brother of Valentinian. Soon, however, the whirligig of Time brought about a strange revenge. Valens himself perished in the awful catastrophe of Hadrianople, the battle in which the Visigoths utterly routed a great Roman army, the battle which first brought home to the minds of men the possibility of the collapse of the Roman empire. The nephew of Valens, the young and generous Gratian, looking round for some man who as partner of his throne might avert the menaced ruin, found none more suitable than the son and namesake of the murdered pacifier of Britain, and accordingly, in the year 379, Theodosius (whom historians have surnamed the Great) was hailed as Augustus at Constantinople.
But now did Britain begin to rear that crop of rival emperors who were the curse of Europe during some of the dying days of the western empire. In 383 a general named Maximus, of whom an unfavourable witness, the ecclesiastic Orosius, testifies that he was “vigorous and honest and would have been worthy of the diadem if he had not, to obtain it, broken his oath of loyalty” was almost against his will declared emperor by the army. He crossed over into Gaul, carrying with him no doubt the bulk of his army. He skilfully played on the disaffection of Gratian’s legions, offended at the partiality which he had showed for his barbarian auxiliaries; a general mutiny was organised; Gratian fled for his life, was pursued and murdered near the city of Vienne. For five years Theodosius had to endure the enforced partnership in the empire of his benefactor’s murderer: then in 388 the smouldering hatred broke out into a flame, and after a hard struggle Maximus was defeated and slain at Aquileia, on the northern shore of the Adriatic (388). According to traditions current two centuries later, this usurpation of Maximus and his consequent withdrawal of the British legions in order to vindicate his claims to the empire, were most important factors in the overthrow of Roman power in Britain.
A large army, on paper, still existed in the island. It was probably about the year 402 that the last edition of the Notitia Imperii, that edition which has been handed down to posterity, was issued from the imperial chancery. In this most valuable document—an army list and official directory of both the eastern and western portions of the empire—we still find cohorts of infantry and wings of cavalry stationed per lineam valli (along the line of the Wall) as they had been for three centuries. We may, however, doubt whether any Roman soldiers were actually keeping the line of the Wall so late as 402. It is remarkable that very few coins have been found in the ruins of the camps of a later date than the reign of Gratian (375–83). If there were any such military units still there, they were probably but the ghosts of their former selves.
To understand the political condition of our island at this time we must have recourse to the pages of the Notitia, which elaborately sets forth the various degrees of the civil and military hierarchy of the empire. On one page we find:—
The Illustrious Prætorian Prefect of the Gauls.
“Under his disposition are the Vicarii of Spain, of the Seven Provinces of Gaul and of Britain.”
On a later page:—
“The Spectabilis Vicarius Britanniarum.”