VATICAN CITY -- Two young women -- a Romanian and a Nigerian -- offered a brief but dramatic lesson on the costs of human trafficking when they explained how they had been sold into prostitution.

The testimonials opened a conference in Rome May 15-16 on "21st-Century Slavery," a phenomenon estimated to affect at least 700,000 people worldwide.

Those numbers quickly took on a human face when "Mikhaila" and "Susa," both 18-years-olds who did not want their real identities publicized, spoke to reporters at the start of the conference.

Mikhaila explained how she entered Italy at age 13 after being orphaned in Romania. She had been lured by promises of a better life. But a few days after her arrival, she was dropped off at a Milan nightclub and turned over to a group of men.

"My Calvary began there," she said. At age 14, she was sold for the equivalent of $2,500, and forced into prostitution. She was resold at an auction at age 16 and kept in another house of prostitution.

"For two years, I never saw the light of day," she said. She was discovered there in a police raid and was taken in by the Pope John XXIII community, run by an Italian anti-slavery crusader, Father Oreste Benzi.

Susa told a similar story of a European odyssey that began with high hopes and instead sank deeper into hidden layers of exploitation.

"I left my country because somebody promised me a good job," she said, adding that her parents were poor and her father was sick.

But within weeks, she was handed over to her new Italian "mother," who forced her into prostitution. The woman demanded high earnings each week, or Susa was beaten.

One day the girl asked an Italian man for help. He took her away, but abused her even more, and she discovered she was pregnant. She fled to Father Benzi's community and says the organization is now her family in Italy.

Father Benzi, a speaker at the human trafficking conference, brought some 500 former prostitutes -- most of them from Eastern Europe and Africa -- to Pope John Paul II's general audience at the Vatican May 15. At the end of the audience, the priest took one of them up for a papal blessing.

Father Benzi said the young woman, a Romanian named Irine, told the pope how she was kidnapped as a child and explained that there were many more like her on the street today. She asked for the pope's help in freeing them from the prostitution racket.

In brief remarks during the audience, the pope encouraged the group to "keep walking the path toward full freedom, which is a foundation of human dignity."

At the conference at Rome's Gregorian University, Father Benzi said the biggest problem related to trafficking was the "lack of political will" to take steps against traffickers and prostitutes' clients.

He also expressed his firm opposition to a proposal, supported by some Italian politicians, that would open so-called "Eros centers" in a move to legalize prostitution and take it out of the hands of organized crime.

Father Benzi said supporters of the proposal say it would "clean up the streets," but added: "I am more interested in freeing the slaves."