Maybe the skyline in some little jerkwater cities could be the work of a couple guys alone. Take London, for example: After a huge fire razed much of the town, 17th-century architect Christopher Wren was responsible for designing so many replacement buildings that an inscription on his tomb reads, "Lector, si monumentum requiris, circumspice," which means, "Reader, if you seek his monument, look around."
Here in a real city like Pittsburgh, though, we've got some history -- a wide variety of building styles and architects. About the only monumental structures whose appearance is consistent throughout Downtown are the protruding stomachs of its office workers. And even these designs are the result of efforts by different firms: Coors Brewing, Iron City ...
Of course, some architects have contributed more to the landscape than others. Perhaps the most prominent, if not the most important, of these was 19th-century architect Frederick Osterling. Osterling designed more than a half-dozen Downtown buildings, including such prominent structures as the Union Trust Building (which denizens of Grant Street know for the oddly church-like structures that contain elevator equipment on the roof), the somewhat overwrought Arrot Building on Wood Street, and the old Allegheny County morgue. That last structure was a homage -- or what architectural historian Walter Kidney's book Pittsburgh's Landmark Architecture calls a "lugubriously amusing caricature" -- of H.H. Richardson's Allegheny County Courthouse. That structure is arguably the most significant Downtown, and Osterling apparently had some issues to work out surrounding Richardson: He once proposed "enhancing" the courthouse with a tower so large that it would dwarf the original building.
Another prominent firm was that of MacClure & Spahr, who contributed the original Warner Theater building (of which the Forbes Avenue façade is about all that's left), the Union National Bank -- notable for its rounded corner at the intersection of Fourth and Wood -- and the old headquarters of the Jones & Laughlin building. Located on Ross Street, the old J&L building is now used by the Urban Redevelopment Authority, which uses it to plan attempts to raze other people's historic buildings.
The architectural firm of Longfellow Alden and Harlow built the Duquesne Club and the "Conestoga Building" in Downtown's "First Side" section near the Mon. Several other structures were built by a splinter group, Alden and Harlow. (Longfellow Alden and Harlow were apparently the Crosby Stills Nash & Young of Pittsburgh architecture, except without all the drug abuse, presumably.) The smaller group built several Downtown banks, perhaps most prominently Fourth Avenue's Bank Tower.
These were local firms, for the most part, but some out-of-town architects got work as well. New York-based Trowbridge & Livingston added the Gulf Building, Federal Courthouse and the old Mellon Bank headquarters on Smithfield (which houses an out-of-town retailer, Lord & Taylor -- for now, at least). But perhaps the most prominent out-of-towner was Daniel Burnham, whom architectural historian Franklin Toker calls "Pittsburgh's favorite outsider." Among Burnham's buildings were the Pennsylvanian (the former Pittsburgh station for the Pennsylvania Railroad) and the Oliver Building on Smithfield Street. Burnham also designed Grant Street's Frick Building, a building Frick had constructed just to dwarf that of his onetime business partner, Andrew Carnegie. (Frick had some issues to work through too, it seems.)
Several buildings have been contributed by more modern architects, though rather than win a bunch of commissions over time they tend to do projects that involve putting up several buildings at once. That business strategy allows a firm to cash in before anybody realizes what's happened. That's how you get projects like Gateway Center, designed by architects Otto Eggers and Daniel Higgins. They tossed up a handful of buildings that looked like lawnmower sheds on steroids, and then they split. A similar, but more successful, example can be found at PPG Place, where renowned architect Philip Johnson built a complex of six shimmering structures.
The most prominent structure Downtown, of course, is the US Steel Building, designed by Harrison & Abramovitz. If that building looks familiar to you, there's a reason: As Toker writes in Pittsburgh: An Urban Portrait, another structure -- the old Westinghouse headquarters on Stanwix Street -- was "a trial run for the same architects." Both buildings are boxy structures with less-than-prominent mid-sections, after all. Come to think of it, more of us beer-swilling Pittsburghers could stand to use it as a model.