It can therefore be readily understood what determined the sudden change between 1140-1150, resulting in that wonderful accession of beauty to architectural design which we find in the Gothic. The incentive had to be a strong one, and of an eminently religious character, to accomplish the radical change of throwing over so absolutely the Norman, and commencing to build entirely on what are called Gothic lines. A careful examination of the proportions of the structures themselves, and the character of the decorations found in the finest examples of buildings representing that style, at once shows us that the incentive was the symbolism attached to the mysterious figure called the Vesica Piscis, which appears to be not only the principal feature upon which the whole style rests, but is also employed, as a symbol of the Divine, wherever we have Gothic Architecture, either in painted windows or mural decorations. Every Cathedral has its Vesica Piscis, often of enormous dimensions. Geometry was synonymous with Masonry, and the very _foundation_ of the Science of Geometry, as expounded by Euclid, was his _first_ proposition. _Every single problem_ in the whole of his books necessitates for its construction the use of this one foundation--namely, "how to form an Equilateral Triangle," and this is the Mystical form of "the Knowledge of the Square." This triangle, symbolising the Logos, is therefore not only the _beginning_ of the Science of Geometry, and therefore of Masonry, the Head of all the Sciences, but it is by that triangle that all Geometrical forms, and therefore forms of knowledge, are _made_, and it became the most mysterious and secret symbol of the Logos, for is it not written by St. John that "In the beginning was the Logos, and by it were all things made"; so the Vesica Piscis, the cradle of the Logos, became the great _secret_ of Masonry, the foundation as we find it upon which Gothic Architecture was evolved, the means by which its wonderful plans were laid down, and the most reverenced figure in Religious Symbolism, as shown by its use in seals, engravings, sculptures, pictures, &c., throughout the Middle Ages.