It is a heady, even historic occasion when, on one and the same day, three leading architectural firms unveil their visions for three of the newest and tallest buildings in the world. Any one of the designs released yesterday for Towers 2, 3, and 4 of the World Trade Center site would, in terms of the size of each project, qualify as a very big deal. Made public virtually on the eve of the fifth anniversary of the terrorist attacks of September 11, 2001, they change the general assessment of the redevelopment of Lower Manhattan.

In terms of design, none of the buildings, which are to rise along a resurrected Greenwich Street, is outstanding or even self-consciously “iconic,” to use the buzz word of the hour. That is, they are not blatant in striving to make a self-serving and unmistakable mark on the skyline of Manhattan.This is understandable, given that their job is to play second, third, and fourth fiddle to the Freedom Tower, which will eventually cow them into subservience. And yet, none of them is bad — which is already something in New York — and each demonstrates a certain grace and distinction.

More important, perhaps, each of the towers has its own personality and its own style. In part we may thank David Childs, the principal architect at Skidmore, Owings & Merrill. It is said that the developer, Larry Silverstein, offered him the project not only to redesign the Freedom Tower, which he has done with distinction, but also to design the remaining towers. These he declined to do, we are told, because he believed that the site as a whole would profit from a diversity of styles. To that end, Norman Foster, Richard Rogers, and Fumihiko Maki were chosen to design one tower each. (The name of the designer of Tower 5 has not yet been made public, if he or she has indeed been chosen, but rumor has it that Jean Nouvel is at the top of the list.)

Surely there is a common thread to the three designs. None of them is even remotely historicist, as they would have been 20 years ago, and none of them is importantly deconstructivist, as they would have been only three years ago, when the WTC master plan was up for grabs. Instead they are very much 21st-century variations on the 20th-century office tower. In all the millions of square feet that these three buildings will contain, there is not a single curving line in sight. Instead one finds a general mood of decorous geometric integrity, especially in Mr. Maki’s project, which exhibits the cool planarity that is typical of recent Japanese projects in New York, such as Yoshio Taniguchi’s new design for the Museum of Modern Art and Sanaa’s design for the soon to be completed New Museum on the Bowery.

As for the two other designs, each exhibits in some measure the perennial preoccupations of the firm that created it. Mr. Foster’s project for Tower 2 will evidently read like two or even four closely contiguous structures. Even if they will spare us the immodest spectacle of those “kissing towers” that he originally envisaged for the site, they seem, at the very least, to be exchanging saucy looks. Their summits appear to be sheared off to produce diamond-like forms that recall the lozenges Mr. Foster has used most conspicuously in his recently completed Hearst Tower at Eighth Avenue and 57th Street.

Mr. Rogers’s contribution appears, for now, to be the least distinguished of the three. Its most conspicuous details are a variety of floor plates fitted into a tower criss-crossed by diagonal girders and culminating in four antennae at each corner of the roof. Through these design elements, Mr. Rogers reveals that ongoing preoccupation with industrialized structural clarity as ornament that was first announced to the world at the Centre Pompidou 30 years ago and that is also seen, in far tamer form, in his new designs for the Javits Center on the far west side.

In part these three designs are a direct function of the close involvement of the developer, Mr. Silverstein. This man lives and breathes real estate, the way the architects live and breathe design. Far beyond the simple desire to build something that will collect rents, he seems to understand, at a far higher level of abstraction than anyone else, how the subtlest shifts in floor plates, sightlines and interactions with the street will enhance the ultimate rentability of his developments. There is nothing wrong with this hard-nosed and mercantile concern. It is responsible for much of the best architecture in New York City and, in the current instance, it has spared us some of the more exorbitant inanities to which architects are driven when left to their own devices. When the history of the designs at ground zero is eventually written, his input will be scarcely less important than that of the architectural firms themselves.

Finally, and perhaps most important of all, the three designs allow us to understand and admire the intelligence of Daniel Libeskind’s master plan. Starting with the 1,776-foot Freedom Tower, their heights form a descending spiral around the memorial, a spiral that will eventually culminate in Tower 5. It is far too early to predict the outcome, but that downward spiral may prove to be the most inspired and unprecedented aspect of the entire redevelopment of Lower Manhattan.