Christianity is a religion frayed over the centuries into many denominations. On Sunday, Pope Francis and the head of a major one vowed to heal one of the church's oldest splits, reports GHN based on CNN.
The Great Schism of 1054 separated the Catholic and Eastern Orthodox churches. Both profess similar doctrine and worship in similar ways, but a millennium ago, Eastern Orthodoxy rejected the ultimate authority of the Pope.
Francis and Patriarch Bartholomew I -- the spiritual leader of some 300 million Orthodox Christians worldwide -- signed a declaration on Sunday committing to unity between the two churches.
Together, they celebrated a divine liturgy at the Patriarchal Church of St. George in Istanbul on Francis' last day in the predominantly Muslim nation -- his first trip there.
Somber intonations and hymns reverberated through the church as the two spiritual leaders prayed and offered reflections and Francis tried to allay worries.
Neither church will submit to nor assimilate the other, the Pope said in his homily, but they will work "towards the restoration of full Communion."
"I want to assure each one of you here that, to reach the desired goal of full unity, the Catholic Church does not intend to impose any conditions except that of the shared profession of faith," Francis said.
He was at St. George's at the Patriarch's invitation, which he extended shortly after Francis' inauguration.
Sunday's celebrations marked the feast of St. Andrew, the founder of the Eastern Church. He was also the older brother of St. Peter, the founding father of the Catholic Church .