After three years, Stilicho sent assistance to them. He appears to have feared the total loss of Britain to the Romans, and, apparently desirous to make a great effort for its permanent recovery on this occasion, he restored the army of Britain to its usual strength, consisting of three legions—the second, the sixth, and the twentieth—by whom the province was effectually freed from the invaders and garrisoned by Roman troops.[99] As long as this army remained in Britain, the province was protected in its full extent to its frontier at the Firths of Forth and Clyde; but the position of the army, as indicated in the Notitia Imperii, sufficiently shows the imminence of the danger which now threatened the province in Britain, and the quarter from whence it was dreaded. The three legions which now protected the frontiers of this distant portion of the Empire, in the last notice which we have regarding the Roman troops in Britain, are found stationed in greatest force along the wall which extended from the Tyne to the Solway, and in the garrisons between that barrier and the Humber, and likewise in those that protected what was now termed the Saxon shore, extending from the Wash to Portsmouth. The ‘Comes Britanniarum’ guarded the western frontier of the two Britains, where the new province of Valentia had probably been formed, with troops which may have been stationed at Caerleon and Chester, the old headquarters of the second and twentieth legions, and the interior of the country is comparatively ungarrisoned. The doom of this great Empire was now, however, rapidly approaching, and the withdrawal of the troops from the remote frontiers to protect the seat of power precipitated the fate of the frontier provinces. The great invasion of the Vandals with the Alani and Suevi, which took place in the year 406, and was the first of those fatal inroads of the Barbarians into the very heart of the Empire which led to its final ruin, alarmed the troops which remained of the army in Britain, who, on the irruption of the Barbarians into Gaul, found that they would be cut off from the other forces of the Empire and exposed alone in their insular position to the attacks of the enemy, and led them to resort to the step which had now become the habitual tendency of a Roman army so placed—to proclaim an Emperor. Accordingly they terminated their four years’ residence in Britain by revolting, and selected Marcus as Emperor. He was soon slain by Gratianus, who assumed the imperial authority, and after a four months’ enjoyment of it, was in his turn slain by the soldiers. [Sidenote: A.D. 407. Constantine proclaimed Emperor; withdraws the army from Britain; third devastation by Picts and Scots.]