subconsciously such a spell upon the minds even of his critics and
detractors, that it resulted in the emancipation of this type of
building from an absurd and impossible convention--the practice,
common before his time, of piling order upon order, like a house
of cards, or by a succession of strongly marked string courses
emphasizing the horizontal dimension of a vertical edifice, thus
vitiating the finest effect of which such a building is capable.

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.]