WHEN the Emperor Diocletian, towards the end of the third century A.D., set himself to reorganize the government of the known world, his stout heart may well have quailed before the magnitude of the task before him. The preceding fourteen years had witnessed a succession of six Emperors, some of them men of exceptional courage and ability, of whom three had been assassinated by their troops, one had been killed by the hardships of campaigning, another by lightning on the borders of Persia, and the last still remained to be dealt with and removed. That task successfully accomplished, Diocletian turned his attention to the greater problem before him, and the conclusion at which he arrived was that in order to save the Empire its constitution must be fundamentally remodeled. His memorable division of the whole into four parts, together with his thorough reform of the administration, enabled the machine of government to run with comparatively little friction for another century and to resist the shattering blows of the barbarian wreckers for many years longer still...