The story of the formation of the first Communes is well known. It is the same in all parts of Western Europe, though the essential characteristics are nowhere more evident than in Belgium. Trade gave the first impulse. It had been practically annihilated by the Norman invasions and the wars of the ninth century. Using the natural waterways of the country and the sea routes, it revived slowly, and we know, through the discovery of Flemish coins in Denmark, Prussia and Russia, that the Belgian coast was already in frequent communication with Northern Europe at the end of the tenth century. The Norman Conquest was the main cause of the rapid progress of trade in the eleventh century. Many Flemings accompanied William in his expedition, many more followed as colonists, and a constant intercourse was established between the Thames and the Scheldt. The development of the trade of Bruges was the natural consequence of the increasing importance of London. Singing the _Kyrie Eleison_, Flemish sailors came up the Thames, bringing to England wine from France and Germany, spices from the East and cloth from Flanders.
Meanwhile, great fairs had been established in Southern Flanders at Lille, Ypres and Douai, where French and Italian merchants met the Flemish traders; so that Flanders was kept in close contact with the romanized countries by the continental routes, while the sea brought her into touch with the Germanic world. Wharves and storehouses were built on the main streams where the merchants made their winter quarters, usually in the vicinity and under the protection of some monastery or some feudal castle. Though the commercial settlements were more dependent than the latter on the geographical features of the country, most of the best situated spots, at the crossing of two main roads (Maestricht), at the confluence of navigable streams (Liége, Ghent), at the highest navigable point of a river (Cambrai), etc., had attracted the monks and the barons before the merchants. The new settlements were, however, quite distinct from the old, and their population lived under an entirely different régime. The name given to them at the time is characteristic: they were called either "porters" or "emporia" (storehouses); even after the industrial population had joined the merchants, the inhabitants remained for a long time "mercatores."