The _pointed_ form of arch was used occasionally in windows during the eleventh and twelfth centuries. But about the beginning of the thirteenth century[171] it began to be employed much more extensively, and in an incredibly short time practically superseded the round arch and became the characteristic feature of a new style, called _Gothic_. The adoption of the pointed arch had very important results. It enabled the builder to make arches of the same height but various widths, and of varying height and the same width. A round arch of a given span can be only half as high as it is wide, but the pointed arch may have a great diversity of proportions. The development of the Gothic style was greatly forwarded by the invention of the "flying buttress." By means of this graceful outside prop it became possible to lighten the masonry of the hitherto massive walls and pierce them with great windows which let a flood of light into the hitherto dark churches.[172] [Illustration: Round and Pointed Arches] [Illustration: FAÇADE OF RHEIMS CATHEDRAL] [Sidenote: Stained glass.] The light from all these great windows might even have been too glaring had it not been for the wonderful stained glass set in exquisite stone tracery with which they were filled. The stained glass of the mediæval cathedral, especially in France, where the glass workers brought their art to the greatest perfection, was one of its chief glories. By far the greater part of this old glass has of course been destroyed, but it is still so highly prized that every bit of it is now carefully preserved, for it has never since been equaled. A window set with odd bits of it pieced together like crazy patch-work is more beautiful, in its rich and jewel-like coloring, than the finest modern work. [Illustration: Flying Buttresses of Notre Dame, Paris] [Sidenote: Sculptured ornament.]