VATICAN CITY — Pope Francis on Christmas Eve formally inaugurates the 2025 Holy Year, reviving an ancient church tradition encouraging the faithful to make pilgrimages to Rome, amid new security fears following a Christmas market attack in Germany.

At the start of Mass, Francis will push open the Holy Door on St. Peter’s Basilica, which will stay open throughout the year to allow the estimated 32 million pilgrims projected to visit Rome to pass through.

The first Holy Year was called in 1300, and in recent times they are generally celebrated every 25 to 50 years.

The last regular Jubilee was in 2000, when St. John Paul II ushered in the church’s third millennium. Francis declared a special Jubilee in 2015-2016 dedicated to mercy and the next one planned is in 2033, to commemorate the anniversary of the crucifixion of Christ.

The Jubilee calendar is a compilation of Holy Year events that will test the stamina of Francis, who just turned 88 and went into the Christmas season with a cold that made it hard for him to catch his breath.

Every month has two, three or four official Jubilee events Francis is expected to attend that are designated for particular categories of people: the armed forces, artists, priests, poor people, volunteers and teachers. Then there are unofficial Jubilee events in which individual dioceses and other groups have organized their own pilgrimages to Rome.

One item on the Jubilee’s unofficial calendar, Sept. 6, has made news because it has been organized by an Italian association, “La Tenda di Gionata” or “Jonathan’s Tent,” which is dedicated to making LGBTQ+ Catholics feel more welcome in the Catholic Church.

Rome Mayor Roberto Gualtieri has said security plans call for a mix of traditional policing — a reported 700 extra officers — plus high-tech surveillance using drones and closed-circuit cameras that keep track in real time of crowd sizes and congestion points using algorithms informed by artificial intelligence.

“There will be more vehicles, more men, and very, very ... shall we say ... robust and important security devices,” Gualtieri told reporters last week.

The Vatican has tried to reduce congestion for pilgrims by allowing them to make advance reservations for visits to St. Peter’s Basilica online.

After a driver plowed into a Christmas market in Magdeburg, Germany on Friday evening, killing five people, Italian authorities sent a circular to police stations around the country recommending “maximum” investigative efforts and to immediately boost surveillance and police patrols in and around Christmas markets and displays and tourist attractions.

The Vatican — with its life-size creche and giant Christmas tree in St. Peter’s Square and outdoor nativity scenes in the Bernini colonnade ringing it — is an at-risk target.

Rome has had two years of intense preparations for the Holy Year that involved major public works projects and artistic renovations coinciding with separate initiatives paid for by the European Union’s COVID-19 recovery funds.

Fewer than a third of the 323 Jubilee projects are finished or will wrap up by next month, meaning traffic headaches and eyesores will continue well into 2025 and even 2026. But Romans and visitors are beginning to see some of the finished products.

Bernini’s fountains in Piazza Navona are glistening white again after a monthslong cleaning. A spiffed-up Trevi Fountain reopened over the weekend, and on Monday the main Jubilee project was unveiled: A pedestrian piazza linking Castel St. Angelo to the Via della Conciliazione, the main boulevard leading to St. Peter’s Square.

Pilgrims who participate can obtain “indulgences” — the centuries-old feature of the Catholic Church related to the forgiveness of sins that roughly amounts to a “get out of Purgatory free” card.

According to church teaching, Catholics who confess their sins are forgiven and therefore released from the eternal or spiritual punishment of damnation. An indulgence is designed to remove the “temporal” punishment of sin that may remain — the consequence of the wrongdoing that may disrupt the sinner’s relationships with others.

Martin Luther’s opposition to the practice of selling indulgences inspired him to launch the Protestant Reformation in the 1500s. He was excommunicated, and the practice of buying and selling indulgences has been illegal since the 1562 Council of Trent. But the granting of them has continued and is an important element in Holy Year pilgrimages.

According to the norms issued for the 2025 Jubilee, Catholics can obtain an indulgence if they:

— Undertake a pious pilgrimage, participating in Masses and other sacraments, at any of the four papal basilicas in Rome or the Holy Land, or other sacred Jubilee sites “so as to manifest the great need for conversion and reconciliation.”

— Participate in works of charity, mercy or penance, such as visiting prisoners or sick or elderly people or undertaking corporal works of mercy “to feed the hungry, give drink to the thirsty, clothe the naked, welcome the stranger, heal the sick, visit the imprisoned and bury the dead.”

— Abstain, in a spirit of penance, for at least one day of the week from “futile distractions,” such as social media, or from “superfluous consumption,” such as fasting; or donating the proportionate sum to the poor or to help migrants.

Francis has long made ministry to prisoners a hallmark of his priestly vocation, and a Holy Year dedicated to a message of hope is no exception.

In fact, the only other Holy Door Francis personally will open this year is at the chapel of Rome’s Rebibbia prison, to draw attention to the need to give prisoners hope of a better future.

The final big event of the Holy Year before it closes on Jan. 6, 2026, is the Jubilee of Prisoners on Dec. 14.