"Buildings without walls:" A tectonic case for two "first" skyscrapers

"A practical architect might not unnaturally conceive the idea of erecting a vast edifice whose frame should be entirely of iron, and clothing the frame--preserving it--by means of a casing of stone... that shell must be regarded only as an envelope, having no function other than supporting itself... "--Viollet-le-Duc, 1868. Viollet-le-Duc's recipe for an encased iron frame foresaw the separation of structural and enclosing functions into discrete systems. This separation is an essential characteristic of skyscrapers today, but at the time of his writing cast iron's brittle nature meant that iron frames could not, on their own, resist lateral forces in tall structures. Instead, tall buildings had to be braced with masonry shear walls, which often also served as environmental enclosure. The commercial availability of steel after the 1880s allowed for self-braced metal frames while parallel advances in glass and terra cotta allowed exterior walls to achieve vanishingly thin proportions. Two Chicago buildings by D.H. Burnham & Co. were the first to match a frame "entirely of iron" with an "envelope" supporting only itself. The Reliance Building (1895) was the first of these, but the Fisher Building (1896) more fully exploited this new constructive typology, eschewing brick entirely, to become the first "building without walls, " a break with millennia of tall construction reliant upon masonry.