The prosperity and power of these communes came from trade, and show how trade prospered and riches accumulated. Some merchant guilds carried on a very extensive business. Take the wool guild of Florence. Tuscany yielded a poor quality of wool, and as it was impossible to weave good cloth from poor wool, these Florentine merchants imported raw wool from Tunis, Barbary, Spain, Flanders, and England, wove it into cloth so deftly that foreigners could not compete with them, and exported it to the principal markets of Europe. Trade with the North, however, was less important than trade with the East. Merchandise was carried over the seas more easily than over the Alps, and in many respects the products of the East were better and more varied than those of northern Europe. The Italians loaded the galleys of Venice, Genoa, and Pisa with silken and woollen stuffs, oil, wine, pitch, tar, and common metals, and brought back from Alexandria, Constantinople, and the ports of Asia Minor and Syria, pearls, gold, spices, sugar, Eastern silk, wool and cotton, goatskins and dyes, and sometimes Eastern slaves. Such a wide commerce outstripped the capacity of barter and cash, and gave rise to a system of banking, with its attendant credits and bills of exchange. The quick-witted Florentines excelled at this business, and great banking houses, like the Bardi and the Peruzzi, had branches or correspondents in all the chief cities. This large commerce in face of the obstacles that barred its way seems extraordinary. A city like Florence, for instance, especially in the earlier days, was greatly hampered by the conditions about her. Outside her walls, within the radius of a dozen or twenty miles, were castles manned by arrogant nobles, who made traffic unsafe. They would not conform to the new economic condition of society except upon compulsion. Rival cities refused to let Florentine wares pass through their territories without payment of ruinous tolls. Wars were waged to moderate these exactions. Or, again, war was necessary to enforce the rights of Florentine citizens in other cities. Moreover, each city had its own system of weights and measures, its own coinage; each imposed customs on all wares entering its gates, in earlier days so much a cart-load, afterwards a percentage of the value. On all highways, at all bridges and fords, there were tolls to be paid. From city to city a merchant had to change his money, until in later times certain coins, like the Florentine florin, passed current everywhere; and sometimes, on entering the gates, he was obliged to adopt a distinguishing badge, as, for instance, according to the usage at Bologna, putting a piece of red wax on his thumb-nail. These were the fetters placed on trade in time of peace; but peace itself was transitory and uncertain. Apart from the wars with the Emperor, the cities periodically fought the feudal nobility, or one another. Venice made war on Ravenna, Pisa on Lucca,