One of the most startling architectural experiences in New York occurs as one walks north on grimy Crosby Street. At Crosby’s northern terminus, at Bleecker, a white cliff of terra-cotta looms into view, slightly off axis. The nearer one approaches, the greater the detail that comes into view. The Bayard Building is like an extraordinary apparition.

The building rose in 1897-99, one of surprisingly few skyscrapers built to the designs of Louis Sullivan. Surprising, because we regard Sullivan as pioneering aesthetic solutions to the difficult design issues raised by the then-new form of the tall metal-framed building. For example, Sullivan extrapolated from the tripartite form of the classical column to design tall buildings with distinct bases, shafts, and “capitals.” (The “solution” seems rather obvious, and it’s unclear to me that others, like New York’s Bruce Price, didn’t hit on this “solution” independently of Sullivan.) Much more important was Sullivan’s sense of how the steel lattice suggested opportunities for dramatic dispositions of elaborate ornamental devices. If Sullivan did not surpass Stanford White as a designer of ornament, White never adapted his ornamental schemes so gracefully to tall buildings.

It is an important point: Sullivan did not employ ornament so as to highlight the building frame, as many people think. Rather, he used the building frame to suggest uses of ornament. Why is this an important distinction? Because for many years, historians hailed Sullivan as the precursor to modernist architects, that is to say, as the first of the tall-building architects to “show off” the undergirding framework of his buildings, foreshadowing the works of such architects as Mies van der Rohe, who designed the Seagram Building on Park Avenue. For years, historians regarded this structural expressionism as the salient feature of Sullivan’s skyscrapers, and paid scant attention to the lavish ornamentation.

Yet what is apparent to anyone who looks at Sullivan’s buildings is that the ornament is what they truly are about. Indeed, Sullivan was a genius designer out of the Arts and Crafts movement, closer to William Morris than to Mies van der Rohe. The historian Paul Johnson ventures, in his “Art: A New History,” to suggest Sullivan as the first great designer of Art Nouveau.

Sullivan famously wished for his tall buildings to “soar,” and so his ornament does not so much “drape” his building as rise up from its base, rather as in a Gothic cathedral. The lush naturalistic ornament rises to a crowning crescendo of terra-cotta angels with wings outspread. Modernist historians of architecture used to suggest that these angels were added, over Sullivan’s objections, by building owner Silas Condict. To think Sullivan capable of such a decorative gesture somehow undermined his modernist bona fides. In fact, we now definitively know that those were Sullivan’s angels. The angels rise up from the piers separating a glorious arcade of five containing-arches of the kind found in 15th-century Italian architecture, though handled here with the utmost originality. Altogether New York boasts no more angelic facade.