(From Mr Hadrian Allcroft’s _Earthwork of England_, by kind permission of Messrs Macmillan & Co.)] It has often been argued that these prehistoric fortresses were merely places of refuge, to which, in time of war, the dwellers in the levels below betook themselves and their flocks. But it is much more probable that they were the permanent habitations of communities, not merely camps, but fixed settlements, chosen for habitation on account of their strong position, and gradually fortified by labour which may have been the work, in the more elaborate examples, of many generations. The need of permanent protection for themselves and their flocks and herds seems to have been felt by the early inhabitants of Britain to such an extent that their regular settlements naturally took the semblance of fortified camps. This is very evident in the case of those camps which are found in positions where the natural advantages are very small—positions which might be chosen by people in search of an abode, but would hardly be chosen merely as a refuge. Camps in these positions are never so imposing as those which crown hill-tops: the labour of excavating the ditches and heaping up the banks was not aided by the natural slope of a hill, and the earthworks, being slighter and nearer the more recent haunts of men, are more liable to destruction. But the defensive nature of such settlements is unmistakable. The Roman invaders brought to England new methods of military construction and the tradition of an architecture of dressed and cemented stone. Their whole system of warfare was far in advance of that pursued by the British tribes. They had developed the art of siege to a high pitch. Their operations in open field were orderly and scientific. Their walled strongholds were constructed with a view which took into account, not only the mere strength of the ramparts, but also the capacity of the defenders to man them. Men, not fortresses, were the main asset of Roman warfare; and consequently their earthwork was far less imposing than that of the Britons of the prehistoric age. Their camps and permanent stations were usually surrounded by a single fosse of no great depth: the rare cases in which traces remain of more than a single fosse are camps upon the exposed northern frontier of Roman Britain, where the onrush of the barbarian enemy was stayed by a series of trenches, either covered with brushwood or filled with sharp stones or stakes. Camps were hastily constructed of earthwork; bank, ditch, and parapet playing their part. But where a camp became a permanent station a stone wall took the place of the earthen bank. The most important relic of the Roman occupation in Britain, the great frontier wall from the Tyne to the Solway, was preceded by a _vallum_ of turf, a temporary defence which was superseded by permanent masonry.