Pope Francis met Monday with the Archbishop of Canterbury Justin Welby where they discussed human-trafficking and modern day slavery and how they can fight it together.

Francis met Welby, who is the most senior bishop in the 88-million strong Anglican communion and the spiritual head of the Church of England and they also discussed Christian unity.

Welby wore an episcopal ring that Pope Paul VI gave to the then Archbishop of Canterbury Michael Ramsey following their meeting in 1966.

At the end of the meeting on Monday the Pope and the Anglican leader prayed together privately.

At his audience with Archbishop Welby, the Pope departed from his official text and spoke in English, The Tablet weekly Catholic publication reported.

"Don't forget the 'three Ps,'" he said. "Prayer, peace and poverty. We must walk together."

Francis said he and the archbishop needed to "stand together" in combating people trafficking, whilst lauding the Anglican leader his leadership in the fight against trafficking and slavery.

"I thank God that, as disciples sent to heal a wounded world, we stand together, with perseverance and determination, in opposing this grave evil," said the Pope.

Welby said to the Pope that in fighting trafficking, he hoped Anglicans and Catholics could join together to bring peace to war-torn parts of the world.

"I marvel at the way God guides frail human vessels to be bearers of the message of salvation, leaving us a legacy across hundreds of years, to which we in our time are called to be faithful.

"I am grateful for the progress that has been made through the generous support of many, to draw to the attention of the world to the evils of Modern Slavery and Human trafficking," Welby said.

The Pope and the archbishop have both decried modern slavery and human trafficking.

The trafficking and enslavement of people generates profits around the world of an estimated $150 billion a year - almost two-thirds of it through sexual exploitation the BBC reported.

The archbishop and the Pope both support the Global Freedom Network, which they announced at their last meeting as a "groundbreaking ecumenical initiative to combat modern slavery and human trafficking." An agreement on the network was signed on 17 March 2014.

"The Global Freedom Network can achieve much practically to dismantle what you have so often rightly said is a grave crime against humanity. It is a crime that we all need to overcome as a matter of urgency, as a matter of human dignity, freedom and wholeness of life," said Welby.

The archbishop, who is on a two-day visit to Rome, on Sunday met with staff and supporters of the Global Freedom Network, the ecumenical-interfaith initiative that is housed within the Pontifical Academy for Sciences