It might be thought that the general expectation of the end of the world in the year 1000, which prevailed towards the end of the 10th century, had something to do with the spread of these wooden castles, as it might have seemed scarcely worth while to build costly structures of stone. But it is not necessary to resort to this hypothesis, because there is quite sufficient evidence to show that long before this forecast of doom was accepted, wood was a very common, if not the commonest, material used in fortification. The reader has only to open his Cæsar to see how familiar wooden towers and wooden palisades were to the Romans; and he has only to study carefully the chronicles of the 9th, 10th, 11th, and 12th centuries to see how all-prevalent this mode of fortification continued to be. The general adoption of the feudal system must have brought about a demand for cheap castles, which was excellently met by the motte with its wooden keep and its stockaded bailey. M. Enlart has pointed out that wooden defences have one important advantage over stone ones, their greater cohesion, which enabled them to resist the blows of the battering-ram better than rubble masonry.[204] Their great disadvantage was their liability to fire; but this was obviated, as in the time of the Romans, by spreading wet hides over the outsides. Stone castles were still built, where money and means were available, as we see from Fulk Nerra's keep at Langeais; but the devastations of the Northmen had decimated the population of Gaul; labour must have been dear, and skilled masons hard to find. In these social and economic reasons we have sufficient cause for the rapid spread of wooden castles in France. The sum of the evidence which we have been reviewing is this: the earliest mottes which we know of were _probably_ built by Thibault-le-Tricheur about the middle of the 10th century. But in the present state of our knowledge we must leave the question of the time and place of their first origin open. The only thing about which we can be certain is that they were the product of feudalism, and cannot have arisen till it had taken root; that is to say, not earlier than the 10th century. CHAPTER VI DISTRIBUTION AND CHARACTERISTICS OF MOTTE-CASTLES