In other words, when decentralization reached its limit, the form of competition changed, and consolidation began. With the reopening of the valley of the Danube, the current turned. At first the tide ran feebly, but after the conquest of the Holy Land the channels of trade altered; capital began to accumulate; and by the thirteenth century money controlled Palestine and Italy, and was rapidly subduing France. Heyd remarked that “the commerce to the Levant took a leap, during the crusades, of which the boldest imagination could hardly have dreamed shortly before,”[125] because the possession of the Syrian ports brought Europe into direct communication with Asia, and accelerated exchanges. From the dawn of European history to the rise of modern London, the Eastern trade has enriched every community where it has centred, and, among others, North Italy in the Middle Ages. Venice, Florence, Genoa, and Pisa were its creations. In the year 452, when the barbarian migrations were flowing over the Roman provinces in steadily increasing volume, the Huns sacked Aquileia, and the inhabitants of the ravaged districts fled for shelter to the islands which lie in the shallow water at the head of the Adriatic. For many generations these fugitives remained poor, subsisting mainly on fish, and selling salt as their only product; but gradually they developed into a race highly adapted to flourish under the conditions which began to prevail after the council of Clermont. Isolated save toward the sea, without agriculture or mines, but two paths were open to them, piracy and commerce: and they excelled in both. By the reign of Charlemagne they were prosperous; and when the closing of the valley of the Danube forced traffic to go by sea, Venice and Amalfi obtained a monopoly of what was left of the Eastern trade. For many years, however, that trade was not highly lucrative. Though Rome always offered a certain market for brocades for vestments and for altar coverings, for incense, and jewels for shrines, ready money was scarce, the West having few products which Asiatics or Africans were willing to take in exchange for their goods. Therefore it was not through enterprises sanctioned by the priesthood, that Venice won in the economic competition which began to prevail in the eleventh century. Venetians prospered because they were bolder and more unscrupulous than their neighbours. They did without compunction what was needful for gain, even when the needful thing was a damnable crime in the eyes of the devout. The valley of the Nile, though fertile, produces neither wood nor iron, nor men of the fighting type; for these the caliphs were ready to pay, and the Venetians provided them all. Even as early as 971 dealings with the common enemy in material of war had reached proportions which not only stimulated the Emperor John Zimisces to energetic diplomatic remonstrance, but made him threaten to burn all the ships he captured laden with suspicious cargoes.