‘For a demonstration of New York at its physical best, go to Broadway between Cedar and Liberty Streets and face east.” So wrote the architecture critic Ada Louise Huxtable in 1968.

It’s 40 years since Ms. Huxtable penned her paean to Liberty Street, and her words still resonate with the architecture buffs of this city.

“This small segment of New York compares in effect and elegance with any celebrated Renaissance plaza or Baroque vista,” she wrote.

On the east side of Broadway between Liberty and Cedar streets is the travertine plaza in front of the 52-story 140 Broadway, designed by Gordon Bunshaft of Skidmore, Owings & Merrill and completed in 1967. Its flush, taut, dark aluminum and glass skin — “gossamer minimums of shining, thin material” — make this the most dramatically sleek Modernist skyscraper in New York.

The plaza is one of the best from the plaza era ushered in by the 1961 zoning code, which allowed floor bonuses to builders who provided public open space. Mies van der Rohe’s Seagram Building (Park Avenue at 52nd Street), completed in 1958, before the new zoning code, showed that the new Modernist towers benefited aesthetically by being set back on elegant plazas.

Unfortunately, most Manhattan plazas are dreary spaces that suck life out of the street. Almost every right-thinking person now believes buildings should be built out to the sidewalk.

But it’s as hard to think that of 140 Broadway as it is of the Seagram Building. The square block (Broadway to Nassau Street, Liberty Street to Cedar Street) that the tower and its plaza occupy is trapezoidal in plan. The plaza wraps around both sides of the building and continues to Nassau Street.

The building’s plan is also trapezoidal, conforming to the site. This allows for a clear sight line, in a slightly southeasterly direction, along Liberty Street from Broadway. A block on, the Federal Reserve Bank of New York, occupying the whole north side of Liberty between Nassau and William streets, is also trapezoidal in plan. And because the bank’s block of Liberty jogs ever so slightly to the south, the bank’s façade fills the eastern vista along Liberty Street in the most pleasing way.

It’s this — the way a Modernist plaza opens the vista to the gorgeous Florentine Renaissance palazzo-style bank, designed by York & Sawyer and built in 1924 — that stirred Ms. Huxtable, and so many others.

Also stirring is the way the ethereality of 140 Broadway — anchored to this world only by the indisputably present red-orange cube, by Isamu Noguchi, in its Broadway-facing plaza — plays off the fortresslike solidity of the bank’s rusticated stone walls, creating that piquant yet apposite mating of the old and the new that, at its best (as here), defines Manhattan urbanism.

Walling the south side of 140’s plaza is the gargantuan 120 Broadway, the former Equitable Building, from 1915. This was the largest office building in the world when it was built. At 40 stories, it was far from the tallest building in the city. But its whopping 1.8 million square feet of floor area makes it still a giant-class building, and its floor area ratio (or ratio of square feet of floor area to the size of the plot) comes in at an eye-popping 30-to-1. By contrast, the notoriously humongous 200 Park Ave. (the former Pan Am Building, completed in 1963), with about a million more square feet than 120 Broadway, has a floor area ratio of 18-to-1.

That said, 120 Broadway, designed by the gifted Peirce Anderson of Graham, Burnham & Co., has a masonry solidity that also plays beautifully off of the “gossamer” 140 Broadway.

Across Nassau Street from 140 Broadway stands another Gordon Bunshaft tower, the 60-story One Chase Manhattan Plaza. Completed in 1961, this was the first glass-curtain-wall skyscraper in the financial district. At the time, the financial district was in crisis (as when has it not been?) as banks and financial services companies were pulling up stakes and moving to Midtown. One Chase Manhattan was David Rockefeller’s vote of confidence in downtown, or something like that.

This is a more strictly “Miesian” building than 140 Broadway. That is, it has that muscular structural expressionism that Mies refined in such works as the Seagram Building, with external aluminum piers pretending to be the actual structural supports of the building. (Frank Lloyd Wright once famously called Skidmore, Owings & Merrill the “three blind Mies.”)

Here too is a plaza. As Ms. Huxtable pointed out, it’s a shame that a sharp change in ground level prevented a natural flow from the 140 plaza to the Chase Manhattan one. Chase’s plaza is adorned with a sunken rock garden by the ubiquitous Noguchi, as well as the papier-mâché-seeming sculpture “Group of Four Trees” by Jean Dubuffet.

The Chase tower lacks 140’s lighter-than-air feeling, and so it contrasts less excitingly with the buildings around it. That said, the south side of Chase’s plaza is walled by the rear of the Trump Building, originally the Bank of the Manhattan (precursor of Chase Manhattan), at 40 Wall St. For a brief time in 1929, this was the world’s tallest building.

“These few blocks,” Ms. Huxtable wrote, “provide (why equivocate?) one of the most magnificent examples of 20th-century urbanism anywhere in the world.”

Forty years later, it’s still pretty great.

fmorrone@nysun.com