He was indefatigable in his journeyings through his empire, to reorganize and reform. Every province came under his personal supervision, and traces of his activity are to be met with everywhere. He was also undoubtedly a great builder. The largest temple ever erected in Rome, the temple of Venus and Roma, owes its origin to him, as also do the Pantheon and the Castle of St. Angelo. He was therefore quite capable of conceiving and carrying out such a project as the Great Wall. He visited Britain in person, towards the close of 121 A.D., or early in 122, but the works were only completed after he had left, under the direction of Aulus Platorius Nepos, his proprætor. Antoninus Pius succeeded Hadrian in 138 A.D. He was himself a man of peace, and left the settlement of disturbances to his provincial governors. {15} Under him Lollius Urbicus built the turf wall between the Firths of Forth and Clyde, along the line of the forts of Agricola. This is known as the Antonine Wall. In mediæval times it was called Grahame's Dyke. Britain was very disturbed from 161 A.D. to 193 A.D. during the reigns of Marcus Aurelius, the philosopher, and his son and successor, Commodus. The Wall and its forts and turrets suffered much during this period. Under Septimius Severus there was still trouble, and the Emperor came over in person, in 208 A.D., bringing with him his sons Antoninus and Geta. The former is usually called Caracalla, from a Gallic mantle which he had made fashionable in Rome. Severus was an African by birth, and a soldier by profession, having risen from the ranks, but he was a splendid administrator. On arriving in Britain, he collected troops, repaired the roads, and rebuilt, where necessary, the forts and the Wall. Then we have a pathetic picture of the old Emperor, hampered by gout, and obliged to be carried in a litter or a closed chair, distracted by the quarrels and ambition of his sons, and yet advancing far into the enemy's country, under inconceivable difficulties, and with a great loss of men. Finally he died at York, in 211 A.D., "worn out with sorrow more than with disease." It is said of him that he had "a greater tenderness for his children {16} than for the republic;" and yet it was no secret that his elder son had once endeavoured to stab him in the back, and, failing, had tried to bribe his physicians to poison him. On their father's death the sons returned to Rome, to succeed him, but in less than a year the elder had contrived the murder of the younger. The inscribed stones which have been found bring out very clearly that Severus left behind him an impulse towards the restoration of the Wall and its forts which continued until 240 A.D. Britain was now left to herself. Rome was too much occupied with troubles at home to pay much heed to her island province, and peaceful conditions prevailed.