Crowds gathered at the Vatican on Thursday to attend the funeral of Pope Emeritus Benedict XVI, hours before the ceremony is set to begin at 9:30 am local time (3:30 am EST).

Mourners filled St. Peter’s Square before the Mass, which will be presided over by Pope Francis. The event, in which a living Pope will lead the farewell of his predecessor, is unprecedented in modern times.

Benedict, who passed away on New Year’s Eve at the age of 95, shocked the Catholic Church when he retired in 2013, becoming the first pontiff to do so in 600 years. He ceded the papacy to Francis, whom he considers a more reformist leader.

Because Benedict XVI was no longer head of state when he died, only two countries, Italy and his native Germany, will send official delegations to the funeral. But other world leaders and royals are expected to attend in a private capacity.

Strong security measures have been put in place at the Holy See to ensure the safety of the event, with more than 1,000 Italian security personnel deployed and its airspace closed during the day.

Nearly 200,000 people have paid their respects to the body of the pope in St. Peter’s Basilica from Monday to Wednesday night.

The Pope’s body has been placed in a simple wooden coffin in preparation for the funeral. After the funeral ceremony, the coffin will be carried back into the basilica and zinc-coated before being sealed in a second wooden coffin.

At his request, Benedict will be buried in the Vatican’s underground grottoes in the niche where first Pope John XXIII and then John Paul II were buried before their remains were moved to more prominent places in the basilica above. A written account of the pope’s life will be buried with him in his coffin, the Vatican announced Tuesday.

Pope Francis praised the late pope emeritus as a «great teacher of catechesis» at a general audience at the Vatican on Wednesday, paying special tribute to his «sharp and gentle thinking.»

Among the prominent clerics who will attend the funeral will be Hong Kong Cardinal Joseph Zen, his secretary said. Zen, a 90-year-old retired bishop, has been at odds with Francis over the Vatican’s agreement with Chinese authorities over the appointment of bishops.

Born in a small Bavarian town, the Pope formerly known as Joseph Ratzinger joined the priesthood in 1951 and rose to lead the Catholic Church in 2005. He was widely considered a supporter of Church conservatives, but the end of his time as pontiff it was clouded. over the church sexual abuse scandal.

Reuters Y Associated Press contributed.