One week after a gathering of biker gangs in Texas resulted in nine deaths and 170 arrests after a shootout, thousands of motorcycle riders roared into the nation's capital Sunday to honor military veterans, prisoners of war and soldiers missing in action.

Rolling Thunder, an annual event that has been bringing motorcyclists and spectators to the National Mall in downtown Washington since 1988, started the "Ride for Freedom" at the Pentagon in Virginia, crossed the Potomac River over the Memorial Bridge and circled the Mall.

Organizers estimated that more than a million bikers and spectators attended, making it the largest one-day motorcycle gathering in the world, Rolling Thunder spokeswoman Nancy Regg said.