Hence the earthwork and the parapet of rock, singly or combined, may be regarded as the first of all castellation, with an origin so remote as to be practically coeval with man's first appearance upon earth. These simple means of defence are found in every country occupied by primitive races; in America they are numerous and undoubtedly point to a high antiquity, and the same holds good in many parts of Asia and Europe. In the British Isles we have a richer collection probably than can be found in any other portion of the globe, for in the habitable districts hardly a square mile exists without some indication of disturbance of the soil due in the majority of cases to some work of a defensive character. Earthworks are of such a varied nature, with so many differences of contrast alike as regards shape, elevation and area, that to the ordinary observer any classification seems impossible, and practically it is only when descriptions and plans of the whole are aggregated for selection that they fall under different headings by presenting essential features common to a class. Hence in late years a system of differentiation has been evolved, and the allocation of an earthwork to a definite class is now possible. To the antiquary this is a source of keen satisfaction, and it is hoped that to the ordinary observer it may prove one of equal interest. It should be borne in mind that earthworks of great antiquity are found only in those districts and localities where man could delve with his primitive appliances, and thus a classification presents itself at once in a contradistinction between the Western and Central parts of England compared with the Southern and Eastern. It is obvious that no primitive race, with their crude appliances, could dig into Cambrian, Silurian, or Carboniferous rock in order to entrench themselves, and that in those localities the breastwork would necessarily be paramount; and that entrenching would only be possible where an accumulation of detritus or alluvium existed, that is to say, in the valleys. So that, broadly speaking, the parapet prevails in Wales and the Midland counties and the ditch in the remaining portions. Those districts, reaching approximately from Dorsetshire to Yorkshire and belonging to the Cretaceous formation, would therefore roughly divide the country into two portions--the fosse prevailing to the east of it, and the breastwork to the west.