As Christians around the world prepared to celebrate the religious holiday, several hundred Iraqi Christians were celebrating Christmas Eve Mass in their hometown near Mosul as both a sign of hope and defiance.
Once home to thousands of Assyrian Christians, Bartella, on the outskirts of Mosul in Nineveh province, fell to Islamic State (IS) militants in August 2014.
IS ransacked the Mar Shimoni church, destroying crosses and removing religious icons and other fixtures, before setting it alight.
WATCH: Iraqi Christians, Pushed From Town by IS, Return for Christmas Eve Mass
Iraqi forces freed Bartella in October as part of an ongoing campaign to liberate nearby Mosul. But residents have not been able to return; much of the town has been destroyed in recent fighting, and basic services are lacking. The militants also planted bombs in the city.
Worshippers were bused to the town from the Iraqi Kurdish regional capital of Irbil, where they have been living.
As bells pealed before the service, women joyously ululated when they stepped into the church. Almost everyone held a lit candle during the service, which was conducted in Aramaic and Arabic.
"It is a mix of sadness and happiness," Bishop Mussa Shemani told Reuters before celebrating the Christmas Eve Mass. "We are sad to see what has been done to our holiest places by our own countrymen, but at the same time we are happy to celebrate the first Mass after two years."
At the end of the service, however, Assyrian priest Yacoub Saady said, "This is the Mass of defiance. We, the Christians, are the oldest component of this country. We are staying put and no power can force us to leave."
Roughly a dozen U.S. military servicemen and a 100-man contingent from the Iraqi military also attended the service in a sign of solidarity with the worshippers.
Volunteers had worked to clean the church for the service, its first since IS militants took over 2½ years ago. For many of the worshippers, the sight of Bartella, once a vibrant town of 25,000, was shocking. Only a few homes stand unscathed. Most have been damaged by shelling or blackened by fire.
Even with the distant sounds of explosions, however, many residents were happy to enter their town and church again.
"Our joy is bigger than our sadness," said university student Nevine Ibrahim, 20, who returned to Bartella Saturday for the first time since she, her parents and four siblings left in 2014. Their house was badly damaged; everything they owned was gone.
"I don't think we can return. The house can be fixed, but the pain inside us cannot," she said, seated among three of her siblings. "Who will protect us?"
Altar boy Masar Jalal, 16, and his father attended Mass on Saturday. It was Masar's first visit to Bartella since he fled with his family to Irbil in 2014.
"I cried for what has become of the town," Jalal told the Associated Press. "I will only come back to live here if there is security."
Elsewhere Saturday, security measures were heightened in Rome, where Pope Francis celebrated Christmas Eve Mass in a packed St. Peter's Basilica. On Friday, the man believed responsible for the Berlin market attack was killed near Milan.
Francis has spent much of this year pleading for the world to better protect innocents caught up in wars, migrations and abject poverty. He also told Christians that materialism has "taken Christmas hostage. ... We have to set it free."
The late-night Mass was the first major event of the Christmas season. It will be followed by Francis' noon Urbi et Orbi (To the city and the world) blessing on Christmas Day.
In Bethlehem, Palestinian boy and girl scouts kicked off Christmas celebrations in the West Bank town with a festive march through Manger Square. The marchers carried Palestinian flags as they passed a giant Christmas tree decked out in gold, in front of the ancient Church of the Nativity.
Pilgrims from around the world watched the outdoor festivities, while inside the 4th century church, they waited in long lines to visit the Grotto of the Nativity, where tradition says Jesus was born.
More than 1,000 congregants attended midnight Mass at St. Patrick's Cathedral, the seat of the Roman Catholic Archdiocese in Karachi. Father Mario Rodrigues emphasized that Christmas was a time to strive for peace across the world.
In London on Sunday, Archbishop of Canterbury Justin Welby, the spiritual leader of the Church of England and the global communion of 85 million Anglican Christians, planned to say in his Christmas Day sermon that 2016 had left the world "more awash with fear and division."
Welby, who was to deliver his sermon at the Canterbury Cathedral in southeast England, was to say the world's values were "in the wrong place, with economic, technological and communications progress failing to deliver justice."
"The end of 2016 finds us all in a different kind of world — one less predictable and certain, which feels more awash with fear and division," he was to say.
Robert Berger in Bethlehem contributed to this report.