The program, titled "Beyond the Wall: A Symposium on Mass Incarceration," featured activists, artists, corrections officials, students, and others.
Martin said there are 2.3 million people in prison nationwide and 5.7 million under "criminal justice supervision," most on probation and parole.
Robyn Buseman, director of the Mural Arts Program's Restorative Justice Program, which brings arts programs to Graterford Prison and the state's juvenile justice system, said there are more people imprisoned in the United States than in any other country.
Bashirah Abdus Samad, whose son is in prison, described the struggle to keep people out of prison as "the longest war in man's history."
John Wetzel, secretary of the Pennsylvania Department of Corrections, said there are 51,000 men and women in Pennsylvania's 26 prisons.
Wetzel, who lives in Harrisburg, hailed the symposium for bringing a diverse group of people together to talk about incarceration rates.
"We have older people, we have younger people, people who have been incarcerated, professional people," Wetzel said. "So just getting these people to the table is important."
During a panel discussion on "Victim and Community Perspective," Cornell Drummond, 27, tall and with his hair in braids, addressed an audience from his wheelchair.
"I was a gangster at one point," Drummond said. He said he was involved in a gang turf war around 60th Street and Lancaster Avenue in West Philadelphia.
"I got shot and was paralyzed," Drummond said. "That still didn't change me."
He said what changed him was a stint in federal prison. That, he said, made him focus on being a good father to his two daughters.
He cautioned others on the dangers of gang and drug activity.
"My message to young people in the streets is that I have never seen anyone who survived the game," Drummond said.
The symposium also focused on ways in which art can help inmates adjust to life after prison.
In another workshop, titled "Art as a Tool," Jesse Krimes, a Philadelphian who served time in a federal prison in North Carolina for cocaine dealing, said art helped him get through his sentence.
He said other inmates were curious about drawings he was creating in his cell.
"The artwork allowed me to break down barriers very quickly," Krimes said.
Jane Golden, executive director of the Mural Arts Program, said art is an important tool in dealing with "intractable" issues, such as crime, poverty, and unemployment. "We can never discount the role of innovation and creativity," she said.
Golden said she was pleased with the symposium's turnout.
"There is an excitement in the air that is palpable. People have told me that it's great to hear about the issue of reentry from different points of view," Golden said.