The exterior of the Franklin and Armfield Slave Office, which is now the Freedom House Museum in Alexandria. (Ricky Carioti/The Washington Post)

The Alexandria City Council unanimously agreed Tuesday night to make a $63,000 interest-free loan and donate the time and talents of city historians to help save a financially struggling museum housed on the site of the largest slave-trading operation in the pre-Civil War United States.

The short-term loan is intended to prop up Freedom House, a decade-old museum in the basement of the Northern Virginia Urban League headquarters. The money will cover the building’s mortgage through November and a portion of its utilities. The city will work with the Urban League to improve the museum, expand its hours and attract more visitors to the house at 1315 Duke St., through which as many as a million slaves are thought to have passed between 1828 and 1861 on their way to bondage in Mississippi and Louisiana.

The house is what’s left of a compound once owned by the Franklin and Armfield Co., which was the biggest and most successful slave trader in the pre-Civil War United States, historians say.

After the Urban League’s financial straits became known late last fall, the city’s Office of Historic Alexandria proposed opening the museum on Saturday afternoons in February for Black History Month and providing professional staff to guide visitors through the small exhibits. Almost 200 people attended the first two Saturdays this month and another 53 have signed up for the coming Saturday as of Tuesday night, city officials said.

Under the agreement, the city will operate the museum Thursdays through Saturdays, from 1 to 5 p.m., with a $5 admission fee, starting in March.

The short-term loan will eventually be paid back to the city under the terms of the agreement, and the Urban League plans to launch a campaign to raise at least $2.5 million, said Tracey Walker, chair of the league’s board. The league’s offices will continue to occupy the upper floors of the building.

City Council members, while emphasizing their support for the loan, wanted reassurances that the Urban League would be able to pay the money back, noting that the city has multiple budget demands this year. City Manager Mark Jinks said he’s comfortable the loan will be “a solid bridge” for the future.

The talk of repayment was too much for City Council member Willie Bailey (D), who described himself as “a little upset, a little teed off by some of the emails we’ve received that said we should not preserve this.” The council spent hours in 2016, he reminded them, discussing whether to put money into the Murray-Dick-Fawcett House, another historic home in Old Town.

“As a black man on this dais, I come into this building and I look out there and I imagine my ancestors being sold on [Market Square],” he said. “ . . . We sat up here tonight and had proclamations for the George Washington parade, and he owned slaves. Alexandria had the largest slave trade in the United States of America and that part of history needs to be told, too.”

Council member John T. Chapman (D), who runs walking tours of significant African American sites in the city, agreed and noted that while historians have done “a ton of research” on Washington, “we’re just starting to get under the surface of African American history and tell the whole story of Alexandria.”

Other council members agreed on the importance of the museum, saying it’s a national treasure, not just a local one. They then voted to apply to the National Trust for Historic Preservation for a grant to help create a long-term sustainable plan to save the museum.