In a solemn ceremony on Christmas Eve, the 88-year-old pontiff will open the Holy Door, which is otherwise walled up from the inside, and pass through it.
The Catholic Church normally celebrates a Holy Year, also known as a Jubilee Year, every 25 years.
According to Catholic belief, believers can gain forgiveness of their sins through prayer and penance during a Holy Year.
This also includes a pilgrimage to Rome and passing through Holy Doors in the Eternal City.
Catholics can obtain a special grace known as a plenary indulgence, which removes all temporal punishment for sin if requirements are met.
More than 30 million pilgrims and visitors are expected in the Italian capital during the Catholic event, with some estimates as high as 45 million.
Pope Francis recited the Angelus noon prayer this week but appeared by video because of a cold. (AP PHOTO)
Francis will then celebrate the traditional Christmas mass, ringing in the Vatican's Christmas festivities.
The pontiff is expected to use the services to speak out forcefully against war and violence and remember the suffering of the people.
He recently called for a Christmas truce in the face of the wars in the Middle East and Ukraine.
In Bethlehem, traditionally the birthplace of Jesus Christ, the festivities are expected to be subdued this year due to the Gaza war.
The procession from Jerusalem to Bethlehem and the midnight mass in Bethlehem are to take place as usual.
However, festive decorations in the small town in the West Bank and the lighting of a Christmas tree in front of the Church of the Nativity are to be avoided.
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