However complete, and it is usually much the reverse, may be the history of a castle, any knowledge we may desire as to its particulars greatly depends upon what may remain of the structure, either in masonry or earthworks, and to understand these the first thing necessary is a plan, and this is just what is wanting in most guides or handbooks of castles. With a good plan not only the age and much of the details of any castle can be ascertained, but sometimes the work recorded in the Pipe or Fabric rolls may be recognised. Original plans indeed there are none; no doubt the military architects, like their ecclesiastical brethren, drew and worked from designs and plans, but these have not been preserved. No such thing is known to exist as an original design or a working drawing of a Norman or even an Edwardian castle. In ecclesiastical researches, from the known uniformity of the arrangements, this want is scarcely felt, but the plan and details of a castle vary with the disposition of the ground or the caprice of the builder, and although a hall, a kitchen, a chapel, a well, and a barrack are indispensable features in a castle, these parts have nothing of the regularity of position of a nave or choir, a cloister, a chapter-house, or a refectory. Nevertheless, great as is the variety in both the plans and details of castles even of the same age, their architects and engineers worked by certain rules, so that if these be studied a clue will be obtained to the age of the work executed. The dimensions, plan, and profile of the earthworks, the presence, absence, or figure of the keep, the thickness of the walls, the plan, figure, proportion and position of the mural towers, the character of the entrance, the material employed, and the particulars of the masonry, all, if carefully observed, afford a clue to the date of the building or of some of its parts, so that as a general proposition, a Norman castle may be known from one of the early English period, or from those of the first or second Edward, and still more readily from those built in the reign of Richard the Second. What these rules are, in what these differences consist, will appear further on. Mediæval architecture has only been scientifically studied during the last forty or fifty years, and military architecture for a still shorter period. Rickman, who first taught us to read the date of a building in its details, was induced to turn his attention to architecture by the advice of Mr. Blore, who died but the other day.