David Garrard Lowe, a writer and architectural historian whose passion for historic preservation — and in particular for the Beaux-Arts mansions, museums and towers of the Gilded Age — helped stem the tide of urban renewal that was leveling large swaths of American cities in the decades after World War II, died on Sept. 21 in Manhattan. He was 91.

Terence Law, a close friend, confirmed the death, in a hospice.

As a child in Chicago, Mr. Lowe marveled at how architects like Daniel Burnham and Louis Sullivan had refashioned his city in the late 19th century, outfitting its homes, department stores and public buildings in neo-Classical and Baroque splendor, a resplendent mishmash of styles referred to as Beaux-Arts.

But by the 1960s, when he began writing about architecture, many of those buildings were falling victim to the wrecking ball, both in Chicago and in his adopted hometown, New York City.

Like many lovers of the Beaux-Arts era, he was shocked when, in the mid-1960s, developers tore down the original Pennsylvania Station, a sprawling transit hall inspired in part by the Baths of Caracalla in Rome, replaced by a claustrophobic warren of underground passageways below Madison Square Garden.

Everywhere he looked, architecture that spoke to the grandeur of urban life was coming down, replaced largely by anonymous modernist structures. He decided to act.

Mr. Lowe spent years traveling back to Chicago, where in various archives he found photos and other historical materials about the many Beaux-Arts buildings around that city that had since been destroyed.