Since it opened on Labor Day, 1914, a vast post office building has presided over the entire block of Eighth Avenue stretching between 31st and 32nd Streets. It has had multiple names, and as many lifetimes. Between gleaming Boticcino marble walls, gold-leafed ceilings bearing the seals of the International Postal Union’s ten member nations, and the Corinthian colonnade with its Herodotus inscription, the public side of the building announced the Postal Service as a noble enterprise. The interior was scarcely less impressive — nearly an acre of mail-sorting space, a system of pneumatic tubes, mechanized conveyor belts, and a starting staff of 1,667, with an expectation to expand within the 1.4 million total square feet of space. The New York Times declared it “the most elaborate post office in America,” and possibly the largest in the world. Built directly over the train tracks leading to Pennsylvania Station, the post office was the work of the same architects as New York’s grand rail depot, McKim, Mead, and White. The two buildings stood as twin symbols of American progress and industry.

The building’s size and significance only continued to grow. The General Post Office (as it was dubbed in 1918) expanded in 1934 to an annex one block away, connected to the main building by a tunnel. By the mid-1950s, 10,000 people worked in the Eighth Avenue building. In 1967, the Times boasted that Manhattan handled one-tenth of all U.S. mail at Christmastime, as much as the entire country of Belgium. Most of it passed through the General Post Office. But just a year later, articles lamented the outdated hand-sorting technology and held the “imperial gift-wrap job” in disdain. Something more modern was called for. So began the Office’s slow decline. By the end of the century the Postal Service had moved most of its business out of the James A. Farley Post Office Building (renamed in 1982 for the postmaster who oversaw the annex, which closed in 1967). In 2009, for the first time in nearly a century, it ceased 24-hour operations.

The building has endured, relatively unchanged. Penn Station was demolished in 1963 and replaced with a congested, subterranean warren. It was an instant mistake, and New Yorkers have been trying to take it back ever since. Recently, the Farley building has found itself at the center of Penn Station’s redemption story. Senator Daniel Patrick Moynihan was among the first to champion expanding the train station into its old sister-building in 1993. Though nearly every step toward renovation has been the subject of bitter disputes, abrupt reversals, and false starts, the USPS finally sold the Farley building to New York State in 2007.

Now Governor Cuomo has announced a $3 billion, two-phase project that intends to put the Farley at the center of a bustling national network once again. The new plans call for a tunnel connecting Penn Station to a new Farley extension, where soaring glass ceilings will join new construction to the bones of the old Farley building. The post office will remain in the front hall, selling stamps and envelopes under the seals of the Postal Union, but the majority of the building will be given over to Amtrak and the Long Island Railroad for platform access and baggage services, and to developers for retail space. And of course, the building will have a new name, for a new chapter in its history. Below, photographer Margaret Morton guides us through the vacant spaces inside what is poised to become Daniel Patrick Moynihan Train Hall, documenting the fleeting window between two lifetimes. –O.S.