The Byzantine economy was among the most advanced in Europe and the Mediterranean for many centuries. Europe, in particular, was unable to match Byzantine economic strength until late in the Middle Ages. Constantinople was a prime hub in a trading network that at various times extended across nearly all of Eurasia and North Africa, in particular being the primary western terminus of the famous silk road. Some scholars argue that, up until the arrival of the Arabs in the 7th century, the Empire had the most powerful economy in the world. The Arab conquests, however, would represent a substantial reversal of fortunes contributing to a period of decline and stagnation. Constantine V's reforms (c. 765) marked the beginning of a revival that continued until 1204. From the 10th century until the end of the 12th, the Byzantine Empire projected an image of luxury, and the travelers were impressed by the wealth accumulated in the capital. All this changed with the arrival of the Fourth Crusade, which was an economic catastrophe.[127] The Palaiologoi tried to revive the economy, but the late Byzantine state would not gain full control of either the foreign or domestic economic forces. Gradually, it also lost its influence on the modalities of trade and the price mechanisms, and its control over the outflow of precious metals and, according to some scholars, even over the minting of coins.One of the economic foundations of the empire was trade. Textiles must have been by far the most important item of export; silks were certainly imported into Egypt, and appeared also in Bulgaria, and the West.[129] The state strictly controlled both the internal and the international trade, and retained the monopoly of issuing coinage. The government exercised formal control over interest rates, and set the parameters for the activity of the guilds and corporations, in which it had a special interest. The emperor and its officials intervened at times of crisis to ensure the provisioning of the capital, and to keep down the price of cereals. Finally, the government often collected part of the surplus through taxation, and put it back into circulation, through redistribution in the form of salaries to state officials, or in the form of investment in public works.