<P> In 439 the Vandals moved eastward (temporarily abandoning Numidia) and captured Carthage, where they established an independent state with a powerful navy . This brought immediate financial crisis to the Western Empire; the diocese of Africa was prosperous, normally required few troops to keep it secure, contributed large tax revenues, and exported wheat to feed Rome and many other areas . Roman troops assembled in Sicily, but the planned counter-attack never happened . Huns attacked the Eastern empire, and </P> <P> the troops, which had been sent against Genseric, were hastily recalled from Sicily; the garrisons, on the side of Persia, were exhausted; and a military force was collected in Europe, formidable by their arms and numbers, if the generals had understood the science of command, and the soldiers the duty of obedience . The armies of the Eastern empire were vanquished in three successive engagements...From the Hellespont to Thermopylae, and the suburbs of Constantinople, (Attila) ravaged, without resistance, and without mercy, the provinces of Thrace and Macedonia . </P> <P> Attila's invasions of the East were stopped by the walls of Constantinople, and at this heavily fortified Eastern end of the Mediterranean there were no significant barbarian invasions across the sea into the rich southerly areas of Anatolia, the Levant, and Egypt . Despite internal and external threats, and more religious discord than the West, these provinces remained prosperous contributors to tax revenue; despite the ravages of Attila's armies and the extortions of his peace treaties, tax revenue generally continued to be adequate for the essential state functions of the Eastern empire . </P> <P> Genseric settled his Vandals as landowners and in 442 was able to negotiate very favourable peace terms with the Western court . He kept his latest gains and his eldest son Huneric was honoured by betrothal to Princess Eudocia, who carried the legitimacy of the Theodosian dynasty . Huneric's Gothic wife was suspected of trying to poison her father - in - law Genseric; he sent her home without her nose or ears, and his Gothic alliance came to an early end . The Romans regained Numidia, and Rome again received a grain supply from Africa . </P>

What was the only roman institution to survive the collapse of the roman empire