From this time forward, with many vicissitudes of military fortune, the contracted Byzantine State endured in virtue of its industrial and commercial basis and its consequent maritime and military strength, managed with ancient military science against enemies less skilled. The new invention of "Greek fire," like all advances in the use of missiles in warfare, counted for much; but the decisive condition of success was the possession of continuous resources. Justinian, among many measures of mere oppression and restriction, had contrived to introduce from the far East the silk manufacture, which for the ancient and medieval European world was of enormous mercantile importance. Such a staple, and the virtual control of the whole commerce between northern and western Europe and the East, kept Byzantium the greatest trading power in Christendom until the triumph of the Italian republics. Even the Saracen conquests in Asia and Africa did not seriously affect this source of strength; for the Saracen administration, though often wise and energetic, was in Egypt too often convulsed by civil wars to permit of trade flourishing there in any superlative degree. The Byzantines continued to trade with India by the Black Sea and Central Asian route; and their monopolies and imposts, however grievous, were relatively bearable compared with the afflictions of commerce under other powers. As of old, the Greeks or Greek-speaking folk were the traders of the Mediterranean, the Saracen navy never reaching sufficient power to check them; and when finally its remnants took to piracy, they served rather to cut off all weaker competition than to affect the preponderating naval power of the Empire. In this period of prevailing commercial vigour, from the sixth to the eleventh century, the life of the Greek Empire was substantially civic, the rural districts remaining desolate, and agriculture extremely feeble,[297] though the Sclavonian immigrants who now inhabited the Peloponnesus[298] must have lived by that means. Under such circumstances the towns would be fed by imported grain, presumably that of the Crimea; but as they did not grow in size, at least in the case of the capital, their industrial prosperity must have largely depended on the restriction of population, whether by vice, preventive checks, misery, or the sheer unhealthiness of city life, which at the present day prevents so many Eastern cities from maintaining themselves save by influx from the country.[299] It is misleading to point to the legal veto on infanticide as a great Christian reform without taking these things into account. The presumption is that misery, vice, child-exposure, and abortion, rather than prudence, kept the poor population within the limits of subsistence.