Of all the prominent features of architecture that which has been least changeable until late years is the “roof.” The outline of that covering has been limited to a very few ideas, some of which resolved themselves into arbitrary rules of government from which the hardiest adventurer was loath to attempt escape. Deviating from the very general style of roof which on the section presents a triangle, sometimes of one pitch, sometimes of another, but almost universally of a fourth of the span, the _truncated_ form was to be found, but so exceedingly sombre was this peculiar roof that it never obtained to any great extent, and indeed it presented on the exterior a very serious obstacle to its adoption by architects in the difficulty of blending it with any design in which spirit, life, or elegance, was a requisite. There are occasionally to be found in Europe, and even in America, examples of these truncated roofs, but it is very questionable whether there are to be met with any admirers of their effect. The principle on which they are constructed has, however, a very great advantage in the acquirement of head-room in the attics, giving an actual story or story and half to the height, without increasing the elevation of the walls. The architects of the middle ages took a hint from this evident advantage, and used the truncated roof on their largest constructions. Its form is that of a pyramid with the upper portion cut off (_trunco_, to cut off, being its derivation.) MANSART, or as he is more commonly called MANSARD, an erratic but ingenious French architect, in the seventeenth century invented the curb roof, so decided an improvement on the truncated that it became known by his name. This roof adorning the palatial edifices of France soon assumed so much decorative beauty in its curb moulding and base cornice, as well as in the dormers and eyelets with which it was so judiciously pierced, that it became a source of artistic fascination in those days in France; and as Germany was indebted to French architects for her most prominent designs, the Mansard roof found its way there, and into some other parts of Europe. But, much as English architects admired, as a whole, any or all of those superb erections of the Gallic Capital, it was a century and a half before it occurred to them to imitate them even in this most desirable roof.