The beginning and the end of the disaster were successful raids on Italy. Alaric and his Visigoths (401-410 A.D.) shattered the prestige and destroyed the efficiency of the government which ruled in the name of the feeble Honorius. The Ostrogoths under Theodoric destroyed the last simulacrum of an imperial power rooted in Italy (489-493 A.D.). After Theodoric had vanquished Odoacer, it was clear that the western provinces would not again acknowledge an Emperor acclaimed at Ravenna; although the chance remained that they might be reconquered and reorganised from Constantinople. This chance disappeared when the Lombards crossed the Alps (568 A.D.) and descended on the Po valley. From first to last Italy was the key to the West. And these successive shocks to imperial power in Italy were all due to one cause. All three of the invading hordes came from the Danube. The Roman bank of the great river was inadequately garrisoned, and a mistaken policy had colonised the Danubian provinces with Teutonic peoples, none the less dangerous for being the nominal allies (_foederati_) of the Empire. The Visigothic raids, which were in fact decisive, succeeded because the military defences of the Western Empire were already strained to breaking-point; and because the Roman armies were not only outnumbered, but also paralysed by the jealousies of rival statesmen, and divided by the mutinies of generals aspiring to the purple. The initial disasters were irreparable, because the whole machine of Roman officialdom came to a standstill when the guiding hand of Ravenna failed. Hitherto dependent on Italy, the other provinces were now like limbs amputated from the trunk. Here and there a local leader raised the standard of resistance to the barbarians. But a large proportion of the provincials made peace on the best terms they could obtain. Such are the essential facts.