But with their planned parade to Camden Yards blocked by city police for lack of a permit, the protesters apparently didn't make much of an impression on either the pope or the multitudes who had come to see him.
The four dozen or so protesters did rally for about 90 minutes at the Washington Monument and then split up to try to gain attention along the papal parade and other stops of his visit.
Waving signs such as "My God is pro-choice" and "If the Pope could get pregnant, abortion would be a sacrament," the activists criticized the pope's opposition to abortion, birth control and gay and lesbian rights.
"The pope and the Catholic Church are anti-people," said Nick Nichols, 25, a Johns Hopkins University graduate student who ++ said that as a child he had served as an altar boy. "I think that homosexuals deserve the same rights as heterosexuals and that women's rights ought to be respected, and the pope doesn't agree with that. That's why I'm here."
The protesters represented a number of groups, including the National Organization for Women, Workers World Party, All People's Congress, BaltiBARF (bisexual and radical feminists) and Socialist Action.
A march planned from the Washington Monument to Camden Yards -- scheduled to conclude just as the papal Mass finished -- was canceled after Baltimore police said the activists hadn't obtained a parade permit.
The cancellation angered the protesters, who insisted they had a right to march peacefully along the sidewalk. "We should be allowed to march and make our opinion known," said Marc Durham, 30, of the Mount Vernon neighborhood. "I can't believe the pope's visit is interfering with our First Amendment rights."
The activists also staged brief protests along the parade route. As the papal parade made its way down Charles Street, the gay activist group Lesbian Avengers released 500 balloons overhead.
"We want to spread the information that we're people who have rights and the Catholic Church should respect that," said Leslie Gross, 34, of Lutherville.
One woman also sat for more than an hour on a friend's shoulders to hold up an abortion rights sign that said, "Every sperm does not deserve a name."
"I know he saw it, because he looked my way as he came by, but he didn't react at all," said Catherine MacDonald, 35, of Southwest Baltimore. "At least he saw what we had to say."