Though many later cities have Roman substrata, in few cases is there evidence of continuous habitation, let alone functional continuity. The 6th and 7th centuries were the nadir of urban life in the region. Exceptions included Huy and Maastricht, moneying and administrative centres associated with the extension of Frankish power north towards Friesland; other urban nuclei were provided by bishop's seats, Merovingian manors, and abbeys.
The 8th and 9th centuries saw more activity in the Scheldt valley, linked to trading emporia on the coast, and Viking raids "did not cause a long interruption in the evolution of the settlements to cities". Urban developments were typically around abbeys or manors, with their attached artisans and associated markets; there is some evidence of international trade and wool and textile production. The different terms used for settlements are revealing: civitas (a Roman administrative centre), castrum (a fortified area), portus (a commercial settlement on a river), vicus, burg, and so forth.
In the 10th and 11th centuries, the Scheldt valley and Flanders led the way, with increasing numbers of towns as well as expansion of existing ones, seen in the succession of town walls and the creation of new urban parishes. Towns often show evidence for dual centres, one outside a castle or abbey, the other an associated trade settlement. This period also saw the beginnings of urban development in Brabant.
With better documentation, in the 11th and 12th centuries we can follow something of the processes of emancipation and industrialisation and the evolution of merchants' guilds, sworn communes, the Flemish metal and cloth industries, and foreign trade. Comparisons with Italian communes are revealing (here Verhulst critiques Pirenne) and links with Italy in trade and finance were important.
Among the key factors in urbanisation were the social changes associated with the end of the manorial system. Verhulst writes:
"the foundations of the medieval town as we known them in north-west Europe in the late Middle Ages ... were laid during the three crucial centuries which in other respects too determined the face of late medieval and early modern Europe, namely the tenth, eleventh and twelfth centuries. Here we can go along with Pirenne ... the concentration of wealth in the hands of certain social groups or classes was indeed fundamental."The geography of the region, with good communications and agricultural potential, and its political history, with fragmented power centres, were also important factors in its precocious urban development.