Now this type of fort will tell us a good deal about itself if we examine it carefully. In the first place, its character is more pronounced than that of any other class of earthwork. It differs entirely from the great camps which belong to the tribal period. It was evidently not designed to accommodate a mass of people with their flocks and herds. It is small in area, and its citadel, as a rule, is very small indeed. Dr Sophus Müller, the eminent Danish archæologist, when dealing with the specimens of this class of fortification which are to be found in Denmark, made the luminous remark that "the fortresses of prehistoric times are the defences of the _community_, north of the Alps as in the old classical lands. Small castles for an individual and his warrior-band belong to the Middle Ages."[9] These words give the true direction to which we must turn for the interpretation of these earthworks. In the second place, this type presents a peculiar development of plan, such as we do not expect to find in the earliest times in these islands. It has a citadel of a most pronounced type. This alone differentiates it from the prehistoric or Keltic camps which are so abundant in Great Britain. It might be too hasty a generalisation to say that no prehistoric camps have citadels, but as a rule the traverses by which some of these camps are divided appear to have been made for the purpose of separating the cattle from the people, rather than as ultimate retreats in time of war. The early German camps, according to Köhler, have inner enclosures which he thinks were intended for the residence of the chief; but he calls attention to the great difference between these camps and the class we are now considering, in that the inner enclosure is of much greater size.[10] It would appear that some of the fortifications in England which are known or suspected to be Saxon have also these inner enclosures of considerable size (6 acres in the case of Witham), but without any vestige of the hillock which is the principal feature of class (_e_). It is clear, in the third place, that the man who threw up earthworks of this latter class was not only suspicious of his neighbours, but was even suspicious of his own garrison. For the hillock in the great majority of cases is so constructed as to be capable of complete isolation, and capable of defending itself, if necessary, against its own court. Thus it is probable that the force which followed this chieftain was not composed of men of his own blood, in whom he could repose absolute trust; and the earthworks themselves suggest that they are the work of an invader who came to settle in these islands, who employed mercenaries instead of tribesmen, and who had to maintain his settlement by force.