When did the Decline and Fall of the Roman Empire begin? The clear instinct of Gibbon carried on his tale to the fall of its Eastern branch; the formal fall of its Western branch he lived not to see. In our point of view the ages of the so-called decline of the Empire are the ages of its greatest influence; the political decline of Rome, the moment when her strength directly as a power began to fail, might perhaps be placed a little earlier than the date chosen by that great master of us all whose immortal tale none of us can hope to displace. Under Trajan the Empire reached its greatest territorial extent. But we may stop and ask whether conquests like his were not in some sense a sign of coming weakness. The second century of our æra opens with Trajan’s momentary glories; before that century is ended, the day of real conquest is past. Marcus keeps his watch by the Danube with other objects than those with which Drusus had kept his watch by the Rhine. The work of a Roman prince is now, not to press the Roman Terminus forward, but to keep him from falling back. The days of victories and triumphs, the days of conquest in the territorial sense, are still far from being past; but from Marcus to Stilicho, we might say from Marcus to Belisarius and Heraclius, to Nikêphoros and John Tzimiskês, to the Palaiologos who won back Constantinople and the Palaiologos who won back Peloponnêsos, conquest commonly meant simply the recovery of a dominion which had once been held and which had fallen away. We may apply the rule which we applied in our first lecture. When the Greek had to drive back the Persian from Greek soil, when the Roman had to drive back the German from Roman soil, it was a sign that the greatest days of each people, as far as greatness of territorial dominion is concerned, had passed away.