Septimius Severus was old and infirm, but his spirit was still unsubdued. When he entered into Caledonia with his son Caracalla, he brought in his train enormous armaments. His enemies were badly armed; they carried only the short sword and the target, which their descendants in the highlands still employed during the wars of the last century. But they were skilled to take advantage of the natural defences of their country, and without being able to meet the Caledonians in a fixed battle the emperor had lost, it is said, 50,000 men before abandoning his expedition. He had carried the name and arms of the Romans so far that he had no intention of retaining the territory which he had traversed. He left there neither fortress nor garrison, but when he had returned into the subjected territory he separated it from Caledonia by a new rampart, more imposing than all those of his predecessors. For two years the legions were employed in constructing it in stone, fortifying it with towers, and surrounding it with roads. The remains of this gigantic work attest to this day the power of those who raised it. {22} The Caledonians, however, had just attempted another invasion when the emperor, who was marching against them, died at York (211 A.D.), and his son Caracalla, compelled to hasten back to Rome to protect the safety of the empire, hurriedly concluded with the rude tribes a peace which lasted for some years. It was not until the year 228, under the reign of Diocletian and Maximilian, that the dangers which threatened Britain again disturbed the repose of the Emperors. Her shores were threatened by Saxon and Scandinavian pirates. A commander of Belgian origin named Carausius was sent against them, who crowned his success by causing himself to be proclaimed emperor by his legions. Diocletian conferred on him the title of Cæsar. This new sovereign was assassinated at York, and succeeded in the year 297 by his minister Allectus, who himself fell soon after before the power of Constantius Chlorus. When this prince died at York, his son Constantine, proclaimed emperor by his troops, carried with him on leaving Britain a great number of the young men of the country eager to serve in his armies.