The problem of the tall building, with which his predecessors dealt always with trepidation and equivocation, Mr. Sullivan approached with confidence and joy. "What," he asked himself, "is the chief characteristic of the tall office building? It is lofty. This loftiness is to the artist-nature its thrilling aspect. It must be tall. The force of altitude must be in it. It must be every inch a proud and soaring thing, rising in sheer exultation that from bottom to top it is a unit without a dissenting line." The Prudential (Guaranty) building in Buffalo represents the finest concrete embodiment of his idea achieved by Mr. Sullivan. It marks his emancipation from what he calls his "masonry" period, during which he tried, like so many other architects before and since, to make a steel-framed structure look as though it were nothing but a masonry wall perforated with openings--openings too many and too great not to endanger its stability. The keen blade of Mr. Sullivan's mind cut through this contradiction, and in the Prudential building he carried out the idea of a _protective casing_ so successfully that Montgomery Schuyler said of it, "I know of no steel framed building in which the metallic construction is more palpably felt through the envelope of baked clay." [Illustration: PLATE III. THE PRUDENTIAL BUILDING, BUFFALO N.Y.] The present author can speak with all humbleness of the general failure, on the part of the architectural profession, to appreciate the importance of this achievement, for he pleads guilty of day after day having passed the Prudential building, then fresh in the majesty of its soaring lines, and in the wonder of its fire-wrought casing, with eyes and admiration only for the false romanticism of the Erie County Savings Bank, and the empty bombast of the gigantic Ellicott Square. He had not at that period of his life succeeded in living down his architectural training, and as a result the most ignorant layman was in a better position to appraise the relative merits of these three so different incarnations of the building impulse than was he.