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.