A year of mercy has officially begun for Roman Catholics as the church celebrates its year-long Jubilee of Mercy, marked by a ceremony at the Vatican Tuesday.

Pope Francis started the event by pushing open the Holy Door at St. Peter's Basilica before he held a Mass for nearly 70,000 people, Reuters reports. Francis paused to pray before he walked through the door, an act that about 10 million Roman Catholics are expected to imitate in the 700-year-old tradition, according to the New York Times.

"To pass through the Holy Door means to rediscover the infinite mercy of the Father who welcomes everyone and goes out personally to encounter each of them," the pope said during the Mass.

The celebration was watched by about 3,000 soldiers and police who were there to keep the area secure. Aditionally, airspace over most of Rome was closed, and the transfer of specific dangerous goods, including petrol, weapons and fireworks, was banned. There was also a no-go area in force around the Vatican for vehicles, and rubbish bins were either removed or were sealed shut, according to Reuters.

However, Francis encouraged those present to have courage and not to live in fear. "Let us set aside all fear and dread, for these do not befit men and women who are loved," he said. "Instead, let us experience the joy of encountering that grace which transforms all things."

Traditionally, Holy Years have been scheduled to take place every 25 years, but Francis called a special one to promote a more inclusive Catholic church using the theme of mercy to encourage the nearly 1.2 billion Catholics around the world to be less judgmental.

Earlier, the pontiff announced that Holy Doors at various locations around the world would be open, something that has not happened in the history of the Jubilee, according to United Press International. A website that lists cathedrals whose Holy Doors will be open has been published by the Vatican.

The Vatican has also released an official song called "Hymn of the Jubilee of Mercy" in celebration of the Jubilee.

The Year of Mercy will end on Nov. 20, 2016.