In a city where it’s tough to throw a rock without hitting a civic building, it’s easy to pass the Vermont-marble structure at 2215 Constitution Ave. without giving it a second thought. Passersby who do notice the Beaux-Arts building, flanked by classical vases, offset by expansive stairs, and evoking a neoclassical mausoleum, probably mistake it for yet another museum overlooking the Mall.

But that plot on the Mall’s northwest corner since 1934 has been the home of the American Pharmacists Association. The land once belonged to a man nicknamed the “Quinine King” for the antimalarials he sold Union soldiers during the Civil War, and taxi drivers later called the building “the Tomb of the Unknown Pharmacist.” In 1975, Saudi Arabia sought in vain to purchase the plot for its embassy, and in the 1960s, the building was briefly considered but then rejected for the U.S. vice president’s residence when Hubert Humphrey, an APhA member, held the post.

Most intriguingly, however, 2215 Constitution is the only privately held property on the Mall, home to so many other museums and memorials. Though the association stands out among its nearby colleagues, the structure is architecturally congruous with the neighborhood.

The taxi drivers were misinformed, as was the California congressman who also called it “the Tomb of the Unknown Pharmacist” at a 2000 House subcommittee hearing, referring to “that wonderful little building at the end of Constitution Avenue.” The APhA building was initially designed not as a tomb but as the Abraham Lincoln birthplace memorial in Hodgenville, Ky.

The design by John Russell Pope, whose Washington oeuvre includes the Jefferson Memorial, the National Archives and the National Gallery’s West Building, was deemed too costly, so Pope retooled it for APhA; self-plagiarism of this sort was de rigueur at the time. Though tomblike, the building never was intended to memorialize the dead — pharmacist or otherwise.

The association acquired the land and commissioned the building at a time when the Mall didn’t exist as it now does. A canal ran along Constitution Avenue, and part of the plot was underwater when former APhA president John Kidwell bought the swamp land in 1869. It had silted by 1885 when Kidwell died, and the Supreme Court later claimed the land for the government, APhA historian George Griffenhagen said at a 2002 association meeting.

It took 35 years for APhA, founded in 1852, to begin to seek a permanent home. Fundraising started slowly, according to Griffenhagen, and APhA’s 1923 meeting raised just $21,000 for a building — “a ridiculous amount” given the nation’s 52,000 druggists at the time, said the man who would chair the building committee. Three years later, more than $500,000 lay in the coffers, and a vote settled on Washington for the location.

This was the infancy of the Mall. The Lincoln Memorial opened in 1922, and the National Academy of Sciences building was dedicated two years later. APhA acquired the plot between 22nd and 23rd streets — the same one Kidwell had owned — in 1928, and a 1932 act of Congress shut a street cutting diagonally across the land in exchange for APhA’s contribution of other land so 23rd Street could be widened.

Dedicating the new building was an important moment for APhA, which now boasts 62,000 members. An annex added space to the structure in 1960, and in 2009 a second annex increased square footage from 31,000 to nearly 360,000. Today, it rents space to the State Department.

Tourists flocking to the Mall to visit museums and memorials also find the home of a pharmaceutical group with one of the nation’s most prominent footprints, nestled beside the State Department. The central location undoubtedly benefits the association, whose political action committee contributed nearly $145,000 to federal candidates during the 2016 cycle.

APhA gave the maximum permitted contribution, $10,000, to Rep. Earl L. “Buddy” Carter (R-Ga.), the only pharmacist elected to Congress. Carter’s pharmacy businesses have raised questions about conflicts of interest in the past.

The building itself is an artifact of a different era in Washington’s architectural history. It fit into the vision Pierre L’Enfant, of L’Enfant Plaza fame, had for the Mall as a symbolically open space commanding “reciprocity of sight” between memorials and other structures, said Joanne Allen, a professorial lecturer in art history at American University.

“Pope’s modest, restrained classicism conveys a sense of permanence and respectability while allowing for the display of iconography expressive of the aims and progress of the pharmaceutical profession,” Allen said.

The term “Big Pharma” is anachronistic when considering the building’s inception, according to Thomas Luebke, secretary since 2005 of the U.S. Commission of Fine Arts, the federal design-review agency. At the time, no one would have had an inkling of how enormous a part of the economy drugs would become. “It’s ironic,” he said. “It’s interesting that what would have been a tiny little sliver of economic life and interest would have gotten such a prominent thing.”

But prominent it became, and Pope’s APhA building endures. Allen and Luebke agreed that it ought to be considered within a broader architectural landscape, including the former Corcoran Gallery of Art (completed in 1897), the American Red Cross headquarters (1917), Daughters of the American Revolution Memorial Continental Hall (1929), the Organization of American States building (1910) and the National Academy of Sciences.

“They’re all very distinguished buildings, each by fairly distinguished architects, all in a row,” Luebke said.

Correction: An earlier version of this article incorrectly described the building as windowless.