The tower is constructed of an exterior and an interior cylinder of masonry, the space between them being occupied by a spiral staircase. The steps of the latter were individually measured by Professor Goodyear, who has set forth the results in a Bulletin of the Brooklyn Institute of Arts and Sciences (Jan. 21, 1911). Briefly, they show that the treads of the steps vary in height and that they incline sometimes toward the inner wall, sometimes toward the outer. In this way they tend to create a balance of strains on the whole structure, which is further secured by increasing the strength of the inner walls, where the inclination is inward. That the careful calculation involved in this was not due to an afterthought or the necessity of remedying the effects of a settlement is proved by the fact that the inclination begins at the lowest step. Why then was this design adopted? Professor Goodyear furnishes the answer in two subsequent Bulletins. Reduced to briefest terms it is this: The Pisan Baptistry also has an inclination from the normal, both perpendicular and horizontal. Thus, in the south façade there is an inclination in the horizontal lines of 2 feet 2 inches toward the choir. Meanwhile, the vertical lines of the west façade are perpendicular to this slope and, consequently, the front inclines inward toward the nave. And these are only instances of a number of asymmetries that occur throughout the cathedral, all of which are proved to have been intentional in the original design. Further, the asymmetries at Pisa bear a close analogy to the numberless asymmetries that appear in S. Mark’s, Venice. The latter was built by Byzantine workmen, who therein followed the Oriental and the Hellenic dislike of formal mathematical regularity; and it is the Byzantine tradition again which in this respect, as in other details of decoration, domes and so forth, influenced the Romanesque group of buildings at Pisa. The order in which they were erected is, the Cathedral, Baptistry, and Campanile; so that in the Leaning Tower the architects merely carried the principle of asymmetry to an extreme pitch. The influence of Pisa is found in =S. Michele= and =S. Martino= in =Lucca=, and in the =Cathedral of Pistoia=.