Add to these causes the frequent collapses due to mediæval jerry-building, both Norman and Gothic. Many central towers collapsed—_e.g._, at Winchester, Ripon, Wells, Ely, Peterborough, Lincoln; and doubtless there were collapses of many others, of which we have no record. Hence, for example, the fourteenth-century choir of Ely. Whole sections of a cathedral tumbled down—_e.g._, in St. Alban’s nave. The early masonry was but skin-deep; inside the thin casing of masonry the core of piers and walls alike had crumbled into powder; foundations were insufficient, or were simply omitted. The object was, but too often, not to build soundly, but to build a bigger church than the rival over the way, and to hurry it up as quickly as possible. Hence the shocking building done by the Peterborough people in their rivalry with Ely. A considerable amount of space has been devoted to what is called the ichnography of the cathedrals—their ground-plans. It has not been possible to insert plans in the book; it seemed hardly desirable to do so. The _Builder_ has published valuable plans, on a large scale, of all the cathedrals; they can be obtained separately, with the accompanying letterpress and illustrations. The student should never visit a cathedral without one of these plans. (I may add that he should always have a binocular to study the detail, much of which—_e.g._, the bosses—is quite out of the reach of the unaided eye.) As regards the nomenclature of the parts of a cathedral, it may be useful to mention that the high altar is to the east; and that, facing the east, the visitor has the south transept and south aisles on his right, and the north transept and north aisles on his left hand. Standing at the altar or the choir-screen, and looking down the nave to the great doors, he has the north transept and north aisle of the nave on his right, and the south transept and south aisle of the nave on his left. [Illustration: SOUTHWELL CHAPTER-HOUSE.] The western limb of the cathedral is called the nave. The term “choir” is sometimes loosely applied to the whole of the eastern limb. Strictly it applies just to that part of the church where the stalls are; and that part, as in St. Alban’s and Norwich, need not necessarily be in the eastern limb at all, but in the crossing and in the easternmost bays of the nave. In a cathedral with a fully-developed plan,—_e.g._, St. Alban’s or Winchester—the following ritualistic divisions will be met with in passing from west to east:—(1) The nave; (2) the choir; (3) the sanctuary; (4) the retro-choir, containing (_a_) processional aisle, (_b_) Saint’s chapel, (_c_) ante-chapel or vestibule to the Lady chapel; (5) Lady chapel. Sometimes these ritualistic divisions correspond with the architectural divisions of the church; sometimes they do not: _e.g._, the ritualistic divisions of the eastern limbs of York and Lincoln were not shown in the structure, but merely marked off by screens, most of which have been destroyed.