Pope Francis will shine a light on America's broken incarceration system with visit to Philly prison
Pope Francis officiates a holy mass at the square of Christ the Redeemer in Santa Cruz, Bolivia on July 9, 2015 (AFP)

When he visits a Philadelphia jail on Sunday, Pope Francis will offer the world a glimpse into America's broken prison system, where overcrowding and long-term solitary confinement have become commonplace.

The stop by the pontiff will offer a glimmer of humanity to a system housing suspects and convicts who are also some of the poorest members of American society, and where blacks and Hispanics make up a disproportionate majority.

The 25-acre (10-hectare) Curran-Fromhold Correctional Facility, named after a warden and deputy warden murdered in 1973, is the biggest jail in Philadelphia.

Opened in 1995, it appears modern and neat from the outside. The buildings are painted pink, there are well-tended lawns and the parking lot is surrounded with small trees.

But inside the walls topped with barbed wire, the institution offers a window on the problems plaguing the prison system, illustrated by a recent video showing a guard violently hitting a detainee.

There, the pope -- under tight security -- will meet about 100 prisoners, men and women carefully chosen by authorities from across the Philadelphia Prison System by chaplains, social services and security staff.

"Those chosen expressed interest in meeting our 'special guest,' have exhibited good behavior (no infractions) while in custody and demonstrated commitment to attending faith services," prison spokeswoman Shawn Hawes told AFP.

- Chair made in prison -

Francis will sit in a chair made by detainees as he speaks with their relatives.

But there is no planned tour of the facility itself, despite mounting reports in recent years of the ever-worsening quality of life in prisons, including shocking sanitary conditions, with broken toilets or non-existent plumbing.

The situation is so dire that the city of Philadelphia has been sued over the issue.

In one complaint seen by AFP, three inmates were held in cells meant for two, leaving one to sleep in a blue plastic cot on the floor near the toilet.

"During times of overcrowded conditions, triple celling is necessary," Hawes acknowledged, while noting: "The time that inmates are held in triple cells is limited -- they are cycled out into two-man cells within 60 days."

Hawes said Curran-Fromhold currently holds 2,863 inmates, even though it can accommodate "well over" 3,000 prisoners.

More than three-quarters of those in custody are awaiting trial.

These inmates often remain at the facility because they lack the means to pay their bail, even if the fee is just a few hundred dollars.

It is just one example of the ultra-expensive American correctional system that is home to 2.2 million people -- giving the United States a record incarceration rate among developed nations.

In July, Barack Obama became the first sitting US president to visit a federal prison, touring the "B" block of El Reno Federal Correctional Institution in Oklahoma, where he met six inmates convicted of drug offenses.

Obama wants to cut the number of people incarcerated, curb use of solitary confinement and end mandatory minimum sentences.

"We have to consider whether this is the smartest way for us to both control crime and rehabilitate individuals," he said during his visit.

The pope -- a vocal opponent of indefinite solitary confinement, which many countries equate to torture -- has already visited a number of prisons, including Bolivia's most dangerous prison in July.

In the City of Brotherly Love, prison reform activists are especially eager to hear the pontiff speak about the US system, which has been criticized for its use of capital punishment.

In 28 states, prison authorities still shackle women who are pregnant, giving birth or about to give birth, a practice The New York Times said this week amounted to "sheer cruelty and pointless degradation."

The pope's call on Thursday before the US Congress for an end to capital punishment "was said very clearly, at a time when there is movement to end the death penalty," said

Marie Dennis, co-president of Pax Christi International.

"Hopefully, that will also have a positive impact."