Pope Francis opened the Holy Door at St. Peter’s Basilica on Tuesday the 8th of December, marking the beginning of the Jubilee Year of Mercy.

Following him after he walked through the doorway was a frail Emeritus Pope Benedict XVI (88 years), whose resignation in 2013 resulted in the election of Pope Francis’.

More than 10 million pilgrims are expected to pass through the bronze door, which is usually sealed, during the 12-month period. This jubilee year calls on Catholics to reflect on the theme of mercy.

Holy doors will also be opened at cathedrals around the world starting Sunday, for the first time during a Jubilee of Mercy. The pope celebrated a special Mass in St. Peter’s Square before an estimated 50,000 people.

Leading the crowd in prayer, he said: “You cannot conceive of a true Christian who is not merciful, just as you cannot conceive of God without his mercy. Mercy is the key word of the Gospel. … We should not be afraid: We should allow ourselves to be embraced by the mercy of God, who waits for us and forgives everything.”

Pope Francis also asked the throngs of people to send their prayers for Pope Emeritus Benedict’s “good health,” and the crowd responded with cheers.

The last jubilee was in 2000, under St. John Paul II. The jubilee is usually marked every 25 years and many expected the next jubilee to begin in 2025, but the pope can call for an “extraordinary” jubilee.

The pope technically launched the jubilee in the Central African Republic last week, when he opened the Holy Door of the cathedral in the capital Bangui during his historic visit to Africa.

On Tuesday night to mark the occasion, a coalition of humanitarian groups will project images of nature by well-known photographers and filmmakers on the facade of St. Peter’s. The images are inspired by climate change, fauna and human dignity.