We may conclude, then, with every appearance of certainty that the Danish camps were enclosures of large area which very much resembled the larger Roman _castra_, and that, like these, they frequently grew into towns. Placed as they generally were on good havens, or on navigable rivers, they were most suitable places for trade; and it turned out that the Danes, who were a people of great natural aptitudes, had a special aptitude for commerce.[153] Dr Cunningham remarks that they were the leading merchants of the country, and he attributes to them a large share in the development of town life in England.[154] The organisation of their armies was purely military, but at the same time democratic; and when it was applied to a settled life in the new country, the organisation of the town was the form which it took. The Lagmen of Lincoln, Stamford, Cambridge, Chester, and York are a peculiarly Scandinavian institution, which we find still existing at the time of the Domesday Survey.[155] Thus we see that the fortifications of the Danes, like those of the Anglo-Saxons, were the fortifications of the community. And we shall see in the next chapter that this was the general type of the fortifications which were being raised in Western Europe in the 9th century. CHAPTER V THE ORIGIN OF PRIVATE CASTLES We have now seen that history furnishes no instance of the existence of private castles among the Anglo-Saxons or the Danes (previous to the arrival of Edward the Confessor's Norman friends), and we have endeavoured to show that this negative evidence is of great significance. If, assuming that we are right in accepting it as conclusive, we ask why the Anglo-Saxons did not build private castles, the answer is ready to hand in the researches of the late Dr Stubbs, the late Professor Maitland, Dr J. H. Round, and Professor Vinogradoff, which have thrown so much fresh light on the constitutional history of England. These writers have made it clear that whatever tendencies towards feudalism there were in England before the Conquest, the system of military tenure, which is the backbone of feudalism, was introduced into England by William the Conqueror.[156] "Feudalism, in both tenure and government was, so far as it existed in England, brought full-grown from France," says Dr Stubbs; and this statement is not merely supported, but strengthened, by the work of the later writers named.[157] The institutions of the Anglo-Saxons, when they settled in England, were tribal; and though these institutions were in a state of decay in the 11th century, they were not completely superseded by feudal institutions till after the Norman Conquest.