ROME and LONDON -- Pope Francis on Thursday paid homage to his friend and retired predecessor, Pope Emeritus Benedict XVI, by presiding over his funeral mass at the Vatican, an unprecedented event in the modern Catholic Church.
Benedict, who died on Saturday at the age of 95, stunned worshipers in 2013 when he became the first pope to resign in more than 600 years. His funeral marked the first time a supreme pontiff presided over the previous pope's funeral in modern times, according to church scholars.
Thousands gathered in St. Peter's Square on Thursday morning. The funeral procession began before the last of the morning fog had burned off the dome of St. Peter's Basilica, where Benedict had lied in state. The mass began a 9:30 a.m. local time, moments after Benedict's coffin had been carried into the square. Francis arrived in a wheelchair.
Francis opened his homily with Jesus' last words, which were spoken on the cross, saying, "Father, into your hands I commend my spirit." Francis spoke in Italian of the spirit of life that "quietly inspires us," adding that the spirit "wishes to shape the heart of every pastor, until it is attuned to the heart of Christ Jesus."
"Like the Master, a shepherd bears the burden of interceding and the strain of anointing his people, especially in situations where goodness must struggle to prevail and the dignity of our brothers and sisters is threatened," he said.
He also spoke of friendship, likening it to a sustaining force amid a "shipwreck of the present life," as Saint Gregory the Great had written in Pastoral Rule, a guide for leaders.
Francis closed his eulogy by saying, "Benedict, faithful friend of the Bridegroom, may your joy be complete as you hear his voice, now and forever!"
The ceremony had been planned to be "roughly similar" to those held for pontiffs who've died while still leading the church, Vatican spokesperson Matteo Bruni told reporters on Wednesday.
"The missing elements are those most pertinent to a reigning pontiff," Bruni said, "such as the final supplications, the supplication of the diocese of Rome and the Eastern Churches that are very specific to a sitting pope."
Heads of state and Catholic dignitaries attended, although the church offered official invitations to only Italian and German dignitaries. The Vatican advised foreign embassies that any other leaders who wish to attend could do so, but only in their "private capacity."
The United States was represented by Joseph Donnelly, U.S. ambassador to the Holy See, his office said on Thursday. The ambassador represented the U.S. in keeping "with the wishes of both the Vatican, and Pope Emeritus for a simple, solemn funeral," officials said.
Benedict, who was born Joseph Ratzinger in Germany in 1927, had been elevated to pope when he was 78 in 2005. He retired eight years later, citing declining health.
Thousands of worshipers flocked over the last few days to St. Peter's Basilica, where the retired pontiff lied in state in red vestments. Members of the Swiss Guard flanked Benedict, standing just outside the red velvet ropes surrounding his remains.
A constant stream of mourners flowed into the church. Many lined up for hours to pay their last respects. More than 65,000 people were said to have filed into the Basilica on Monday alone, with similar crowds on subsequent days.
The bells at St. Peter's Basilica have not rung since Saturday, the day Benedict died, Vatican officials confirmed. Death tolls are usually rung for the death of a sitting pope.
Benedict's remains were placed on Wednesday in a triple coffin -- lined with cypress, zinc and wood -- and were brought on Thursday at about 8:50 a.m. into St. Peter's Square, where the funeral was to be held.
During the mass, Francis sat and watched as a cardinal anointed and blessed the coffin. Moments earlier, Francis had said in Latin, "May the Blessed Virgin Mary, Queen of the Apostles and Salus Populi Romani, intercede before the Eternal Father, that he may reveal the face of Jesus his Son to Pope Emeritus Benedict and console the Church on her pilgrimage through history as she awaits the Lord’s return."
Francis in the days before and after Benedict's death asked the church's followers to pray for him. The two popes were reportedly friendly following Benedict's resignation.
A Vatican press office official told reporters on Sunday that Francis was "the first" to arrive on Saturday at the Mater Ecclesiae monastery, where Benedict lived within the Vatican walls, after receiving the news of Benedict's death. Bruni said that the pontiff then stayed at the monastery for a time of prayer.
Francis on New Year's Day asked followers to invoke "the intercession of Mary Most Holy for Pope emeritus Benedict XVI."
The pontiff added, "Let us all join together, with one heart and one soul, in thanking God for the gift of this faithful servant of the Gospel and of the Church."
Benedict's remains were to be buried immediately after Thursday's funeral, Vatican officials said.
"In addition," Bruni said, "the coffin will also contain the "rogito," a written text that describes the Pontificate that is placed in a metal cylinder inside the coffin. The Vatican on Thursday issued a copy of the text, a biographical sketch of a few hundred words written in Italian. It describes Benedicts parents, his childhood in Germany, his rise to the top of the church and his resignation.
Underneath the text, it reads: "CORPUS BENEDICTI XVI P.M."
As white-gloved pallbearers picked the coffin up to return it to the Basilica, Francis stepped off the dais with the help of a cane. He blessed the coffin, placed his free hand on it, bowed and closed his eyes for a minute of reflection.
He stood for a moment, until his wheelchair was brought to him.
Benedict was be interred in St. Peter's Crypt, where more than 90 popes have found their final resting place.
ABC News' Clark Bentson contributed to this report.