Every Emperor knows this fact. His memory goes back to those two fearful years 68 and 69 A.D. when first a revolt in Gaul and a mutiny by the Prætorians in Rome overthrew Nero and set up Galba, then a second mutiny of the Prætorians set up Otho, then a revolt of the Rhine legions set up Vitellius, then a counter-revolt by the Danube and Syrian legions set up Vespasian; with the civilian population looking on helplessly, and being almost as helplessly plundered, while decidedly small bodies of professional swordsmen settled the fate of the Empire. Still later they remember how after Domitian’s murder, the Prætorians (whom that despot had caressed and corrupted) forced his successor Nerva to punish the very conspirators to whom Nerva himself owed the throne. Hadrian, in turn, who passes for a very “constitutional” ruler, when his kinsman Trajan died (117 A.D.), allowed himself to be “proclaimed” immediately by the soldiers in the East where he then was. Next he wrote with studious modesty to the Senate begging the Conscript Fathers to “excuse” the zeal of the army and to ratify its action in choosing him Imperator. Every senator knew the blade might soon be at his own neck if he openly opposed confirming the mandate of the legionaries. The army, in short, is the final authority in the Roman Empire. Presently there may even be an Emperor [Septimus Severus about 210 A.D.] who will give his sons direfully blunt and effective counsel: “Enrich the army and then you can do anything.” =263. Army Held under Stiff Discipline and Concentrated on Frontiers.=--Nevertheless at present the army is under a tight rein. Trajan and Hadrian by a mixture of donatives and severity have restored firm discipline. The Roman world functions freely and normally behind the frontier barriers held by the legions, with the great chaos of barbarism tossing harmlessly outside. Furthermore, this army, if very formidable, is, we shall see, decidedly small. It is distributed mainly along the northern and eastern frontiers, with a sizable garrison and guard-corps at Rome. In the arrangement of the army, most of the provinces seem absolutely divested of regular soldiers save those in transit, and their governors only require a good constabulary to arrest brigands and rioters. The collapse of the Jewish insurrection has practically ended the last serious attempt to cast off Roman authority, and the provinces submit not simply because of fear, but because they are now bound to the imperial régime by great cultural and economic interests.[161] In Rome itself, thanks to the presence of the imperial guard, soldiers are frequent sights upon the streets, but in many other great cities of the Empire they are comparative rarities. Their duties are in the frontiers, and their officers know well the demoralization wrought by keeping their men in city garrisons.