The Washington Mall and the Pentagon rumbled with a quarter of millions of motorcycles on Sunday as Rolling Thunder rumbled into the capital.

Rolling Thunder is an annual motorcycle rally that is held in Washington, DC during the Memorial Day weekend to call for the government’s recognition and protection of Prisoners of War (POWs) and those Missing in Action (MIAs). The tribute to American war heroes started out in 1988 with 2,500 participants.

Some 900,000 riders, passengers and spectators traveled from across the country for Memorial Day weekend to pay tribute to veterans and those stilling missing in action.

The annual event started in 1988, when the Vietnam War was still fresh on the nation’s mind.

The first year, 2,500 motorcyclist rode into Washington as a way to remember the thousands of men who were missing in action or believed still held as prisoners of war.

The Washington Mall and the Pentagon rumbled with a quarter of millions of motorcycles on as Rolling Thunder rumbled into the capital

Rolling Thunder has since become an institution.

Motorcycle clubs from across the country flood the capital’s hotels and suburban campgrounds.

Every sort of bike imaginable is represented – from vintage Indians to the newest Harley Davidsons to custom choppers and BMWs.

The mighty procession began in the parking lot of the Pentagon in Arlington, Virginia, at 7 a.m.

The parade route took the thundering motorcycles past the Vietnam Veterans Memorial, the Korean Veterans Memorial and the World War II Veterans Memorial.

The Washington Monument and the Martin Luther King, Jr. Memorial are other prominent sights along the route.

The motorcycle parade ends on the banks of the Potomac River on the National Mall.

The event also features Thunder Alley in downtown Washington DC, which features vendors selling all manner of stickers, pins and patches to commemorate Rolling Thunder.

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