The simple suggestion has often been made that mediaeval towns were merely survivals of older Roman cities or castra. This seems to account for one or two of the larger towns maintained some continuity of institutions throughout the period of barbarian devastations. Religious institutions were frequently active centres of industry and also of trade, just as they were in a barbarous age the repositories and centres of learning, art and culture. Most authorities hold that the Dark Ages were sufficiently devastating in their effects on urban life as to make any considerable continuity from the old towns to the new improbable. The only sharp division between the earlier village and later town was the fact that the latter was an oppidum—a place fortified for protection by its inhabitants with a wall. All authorities agree in ascribing importance to the town wall, to the market, and to the ownership of some land within the town as a condition of burgess-ship.