The flag of Belarus features a thick, horizontal stripe of red atop a more narrow line of green.

But that’s not the flag that Belarusian Americans hoisted outside Philadelphia City Hall on Friday, at a time when their homeland stands as a staunch ally to Russia in its war against Ukraine.

Instead, members of the Belarusian community raised a century-old, red-and-white banner, from an era before their nation became a Soviet republic, a flag that’s become a powerful symbol of resistance to the country’s autocratic president and a bold emblem of support for embattled Ukraine.

“For us, for Belarus, that flag is the only flag of a free Belarus,” said Siarzhuk Shaliga, of Bucks County, a local leader in the Association of Belarusians in America. “The flag that is waving on the Ben Franklin Parkway, the red-and-green one, is a symbol of communism, and a symbol of Belarus participation in aggression against Ukraine.”

The loud, multilingual commemoration drew Belarusian Americans not just from the Philadelphia area but from all over the country. At least three came from California, and one drove nine hours from Charlotte, N.C.

Others traveled from New York, New Jersey, Texas, Florida, Illinois, and Virginia, forming a crowd of about 150, which included supporters from the local Ukrainian, Lithuanian, Polish, and Georgian communities.

“A historic capital of the U.S., the place where freedom was born,” said Hanna Sharko, an activist in the New York chapter of the Belarusian association, who spoke at the event. “It’s important to show we also would like to be a free people in a free country.”

Sharko, 30, who came to the United States a decade ago and works in internet technology, said it was crucial that Belarusians “stand together with Ukraine and we support them in this war, because this is our war, too.”

For the Belarusian diaspora, March 25 marks “Freedom Day,” an unofficial holiday that commemorates the declaration of independence by the Belarusian Democratic Republic in 1918.

The commemoration proved again that wars and movements are waged not just with bullets but with symbols, like the “Z” on the side of Russian tanks — said to be for Za Pobedu, meaning, “For Victory” — and the sunflower, which has become an omnipresent sign of Ukraine’s fight for survival.

This month the Russian flag that flies among the world flags on the Parkway was stolen — twice. And the Belarus flag was vandalized.

European Union President Ursula von der Leyen has called Belarus “the other aggressor in this war,” as its president, Alexander Lukashenko, welcomed Russia to use the nation as a staging ground for military operations and a departure point for planes and troops attacking Ukraine.

”Every Belarusian needs to fight for freedom,” said Vitaly Samsonov, a businessperson who immigrated to the Philadelphia region in 1998. “This flag represents freedom. The old Soviet flag, what does that represent?”

The day had its twists. New regulations bar the raising of unofficial flags at City Hall. So the Belarusians brought their own flagpole, secured in a cement base, and raised the red-and-white flag beside the Philadelphia, Pennsylvania, U.S., and POW flags.

“It’s our symbol of unity with Ukraine,” said Shaliga, a pharmaceutical company manager who came here in 1999, “the only flag of a free Belarus.”

In January, Philadelphia City Council declared March 25 to be Belarusian Heritage Day, to recognize Belarusian American contributions and to support the pro-democracy protests overseas.

Council authorized the red-and-white banner to fly at a ceremonial flag-raising, which tend to be celebratory affairs at which members of Philadelphia’s immigrant communities recognize important dates and events.

At the same time the city administration was facing growing numbers of requests for ceremonies — 40 a year, up from 10 — with little formal guidance on what kinds of flags could be flown. New rules established that only flags recognized by the U.S. State Department would be allowed.

People complained on Friday, but it didn’t dull their enthusiasm.

“We’re going to show our support for Ukraine,” said Maryia Astapenka, 32, of Levittown, who immigrated from Belarus in 2011. Her sister, Tatsiana, 25, came five years later from a homeland she called “a small country with a big dictatorship.”

Belarus is a landlocked nation of 9.4 million people, covering an area slightly smaller than Kansas. It has lots of problems, including one of the world’s highest mortality rates, and an outdated industrial base that’s dependent on subsidized Russian energy.

Today about 57,000 Belarusian immigrants live in the United States, according to the Migration Policy Institute in Washington. Roughly 2,700 make their homes in Philadelphia and the surrounding suburban and South Jersey counties, as do 8,818 Russians and 15,245 Ukrainians.

“I am proud to stand under your true flag,” Iryna Mazur, the honorary consul of Ukraine in Philadelphia, told the crowd. “You have my heart, and you have the support of Ukraine.”

Yellow-and-blue Ukrainian flags flew in a field of red and white. No one raised Belarus’ official red-and-green.

The evolution of the Belarus flag is closely tied to its relationship with the Soviet Union and Russia, and with its people’s yearning for democracy.

After seven decades as a republic of the USSR, Belarus attained its independence in 1991. That lasted only briefly. For the last 28 years the country has been governed by the authoritarian Lukashenko.

He has kept close ties to Russia while imposing harsh restrictions on free speech, the press, and peaceful assembly. The red-and-green flag is similar to the one used when the country was a Soviet republic, absent the hammer and sickle and the red star.

Lukashenko said the “red represents freedom and the sacrifice of the nation’s forefathers, while green represents life,” according to Radio Free Europe. The pattern on the left is traditional, derived from local plants and flowers.

During World War II, the red-and-white flag was used by Belarusian Nazi collaborators, and Lukashenko’s regime has focused on tying the flag to those organizations and that time, ignoring its history before and after the war.

The 1918 flag was briefly reinstated in 1991, then wiped away in a controversial 1995 referendum. Belarus authorities claimed voters had overwhelmingly decided to give the Russian language equal status with Belarusian, to integrate economically with Russia, to allow early elections — and to adopt a new flag.

When Lukashenko claimed victory in a highly disputed 2020 presidential election, maintaining power amid massive, nationwide protests, the red-and-white banner bloomed anew.

On Friday its rise in the city that gave birth to American democracy added special importance to the commemoration, said Nadzeya Norton, president of the Association of Belarusians in America, who traveled here from San Francisco.

“The world,” she said, “has started to hear us.”

Graphics editor John Duchneskie contributed to this article.