Pope Francis has marked the 500th anniversary of the Protestant Reformation by travelling to secular Sweden and encouraging Catholics and Lutherans to move beyond the "errors" of the past and forge greater unity.
Francis and the leaders of the Lutheran World Federation presided over an ecumenical prayer service in the Lund cathedral - the first time a pope has commemorated the anniversary of Martin Luther's revolt with such a symbolically powerful gesture.
Francis quoted Luther and praised him for having restored the centrality of Scripture to the church.
"The spiritual experience of Martin Luther challenges us to remember that apart from God, we can do nothing," Francis said.
Francis and the Lutheran federation president, Bishop Munib Younan, drew sustained applause at the end of the service when they signed a joint declaration pledging to improve relations through dialogue, while working together to heal conflicts, to welcome refugees and care for the planet.
The goal of the theological dialogue, the statement said, was to bring Catholics and Lutherans together at the Eucharistic table.
Disputes over whether Catholics and Lutherans can receive Communion in one another's churches remain an obstacle after five decades of theological talks.
The Protestant Reformation started in 1517 after Luther nailed 95 theses on the church door in the town of Wittenberg, denouncing what he saw as the abuses of the Catholic Church, especially the sale of indulgences.
Pope Leo X excommunicated him, but the church could not stop his teachings from spreading throughout northern Europe or the world.
As Protestantism spread, religious wars erupted, including the Thirty Years War in 1618-48, one of Europe's bloodiest conflicts.
In Sweden, Catholics who rejected the new Lutheran faith were deported or put to death.
As a result, the pope's visit to Sweden to kickstart the year-long Protestant anniversary initially raised eyebrows.
But the Vatican and Lutheran church both insisted the event was no celebration of Luther's revolt. Rather, they stressed it was a solemn commemoration to ask forgiveness for the schism and rejoice that relations have improved in the last five decades.
In alternating prayers in the Lund cathedral, the Catholic and Lutheran leaders lamented the divisions and guilt of the schism and asked forgiveness for the deaths and pain that their divisions caused over history.
"We have the opportunity to mend a critical moment of our history by moving beyond the controversies and disagreements that have often prevented us from understanding one another," Francis said.
"We too must look with love and honesty at our past, recognising error and seeking forgiveness, for God alone is our judge."
After the Lund event, the Vatican and Lutheran delegations rode together on a bus to attend an event highlighting both churches' peace-making and humanitarian efforts. Testimony from refugees and the Catholic bishop of besieged Aleppo, Syria, topped the list of speakers.
Francis continues his visit on Tuesday with a Catholic Mass in the Malmo sports stadium - added in at the last minute after Sweden's tiny Catholic community were upset that Francis was ignoring them and coming only for the Protestant commemoration.
Years ago, Francis spoke harshly of the Protestant reformers. But in the run-up to the trip, he has had only words of praise for Luther. He recently called the German theologian a reformer of his time who rightly criticised a church that was "no model to imitate".
"There was corruption in the church, worldliness, attachment to money and power," Francis told reporters this summer.
These are the same abuses Francis has criticised in the 21st-century Catholic Church he now leads.