Tens of thousands convened under sometimes rainy skies Wednesday for a celebration that was both homage to and echo of the 1963 March on Washington. Umbrellas and plastic ponchos took the place of the mid-century fedoras and skinny ties. But many still talked of recapturing the mood of a day of euphoria amid the chaos and clashes of the 1960s. Obama - flanked by members of King's family, two former Democratic presidents and Oprah Winfrey - spoke beside a cast-iron bell from the church in Birmingham, Ala., where a bomb killed four black girls in September 1963. At 3 p.m., roughly the time of King's seminal address, that bell was rung, as were bells around the country. Forgoing an umbrella in spite of persistent drizzle, Obama then addressed a crowd that extended beyond the Reflecting Pool. Some television networks showed archival footage of the 1963 crowd in split screen, giving the appearance of the modern president speaking across the decades to the grainy black-and-white masses of history. Many celebrants arrived on the Mall after walking the same path of the 250,000 who marched on Aug. 28, 1963, retracing the soft footfalls that helped begin a cultural earthquake and eventually shook apart the bulwarks of legal discrimination against African Americans. There were long lines at the security checkpoints, and some people were treated for heat- related conditions. Additional screeners were deployed to clear the backlog of people waiting to get onto the Mall just before the headline speakers appeared. Eleanor Holmes Norton, the District's nonvoting congressional delegate and one of the organizers of the original march, marveled at the turnout on a wet and muggy workday. Fifty years ago, we had to convince the president to let us come. Today, the president is coming to us," she exulted. Then and now The day was a mix of historical reflections and modern tension. The parents of slain teenager Trayvon Martin joined in singing "Blowin" in the Wind" with Peter Yarrow and Noel Paul Stookey, who had performed the song at the 1963 march as part of the folk trio Peter, Paul and Mary. Rep. John Lewis (D-Ga.), the last living speaker from the original rally, took the microphone again to answer his own fierce call to action five decades earlier. "This moment in our history has been a long time coming, but a change has come," Lewis said. But he warned, as other speakers did, that the progress should not be mistaken for full equality at a time when African Americans face higher unemployment rates, illegal immigrants live in fear and the Supreme Court has voided sections of the Voting Rights Act.