Hundreds of thousands of anti-abortion activists filled the National Mall and streets of Washington D.C. Friday, marking 40 years since the U.S. Supreme Court ruling establishing a constitutional right to abortion.

Religious and political speakers at March for Life, an annual rally to protest the Roe v. Wade court decision, invigorated the crowds with inspirational messages about the importance of their presence at the protest. More than 55 million abortions have been performed in the past 40 years, they noted.

"Forty years ago, people thought opposition to the pro-life movement would eventually disappear," Boston Cardinal Sean P. O'Malley, who chairs the U.S. Conference of Catholic Bishops Committee on Pro-Life Activities. "The march grows stronger every year."

The crowd cheered when O'Malley read a post by Pope Benedict XVI from his personal Twitter account voicing support for the rally: "I join all those marching for life from afar, and pray that political leaders will protect the unborn and promote a culture of life."

Former presidential candidate Rick Santorum said he "chose life" for his daughter, Bella, who has a rare genetic disorder.

"You are the voice of the voiceless," he said in a pre-rally speech. "You are those who stand for love in a world of death. And we are proud to be here with you."

In a video message, House Speaker John A. Boehner told the crowd that he would work toward a bill banning taxpayer funding of abortions.

The majority of this year's participants were teenagers and young adults. Many came in buses chartered by Catholic schools around the nation.

"We are the generation most affected by abortion. We need to make change happen," Ruben, 19, was quoted as saying by The Lutheran Church's Twitter.

Despite the increasing numbers at the March for Life rally, the majority of Americans don't want to see the court completely overturn the Roe v. Wade decision. Sixty-three percent of adults said they oppose overturning the Supreme Court ruling that legalized abortion, according to a poll by the Pew Research Center for the People & the Press and the Pew Research Center's Forum on Religion &Public Life.

The poll also found that different religious groups were divided on whether abortion was considered morally wrong.

"Most white evangelical Protestants (73 percent), as well as 55 percent of white Catholics and 53 percent of black Protestants, say it is morally wrong to have an abortion. That compares with 36 percent of white mainline Protestants and just 20 percent of the religiously unaffiliated," read the report.