A hundred years ago, in Fatima, Portugal, two children were said to have received the first of several visions of the Virgin Mary while they were tending their family’s sheep. The children, Francisco and Jacinta Marto, died young, victims of the Spanish flu epidemic that was devastating Europe, but their little town became a gathering place for countless pilgrims. On Saturday, the two were canonized by Pope Francis in a large outdoor mass in Fatima, becoming the youngest saints in Catholic history who were not martyrs.

A crowd of around half a million people gathered for the occasion outside the Sanctuary of Our Lady of Fatima, the epicenter of the small Portuguese farm town. The sanctuary attracts millions of religious devotees each year, making it one of the world’s most visited shrines dedicated to the Virgin Mary. Many visitors slept outdoors in anticipation of Saturday’s mass, with some choosing to arrive days earlier to pray at the shrine and recite rosaries in front of a statue of the Virgin Mary. Before delivering the mass, Pope Francis also prayed before the tombs of the Marto siblings.

The pope proclaimed the siblings’s sainthood at the start of the mass, generating widespread applause from the crowd. “We can take as our examples Saint Francisco and Saint Jacinta, whom the Virgin Mary introduced into the immense ocean of God’s light and taught to adore him,” the pope said. “That was the source of their strength in overcoming opposition and suffering.”

At ages nine and seven, Francisco and Jacinta, along with their older cousin, Lucia Dos Santos, were said to have received three messages from the Virgin Mary. These messages were later regarded as “the secrets of Fatima.” The first two secrets allegedly referred to visions of hell, which believers take to be a prediction of communism and World War II. The third secret was the source of speculation for many years, before the Vatican declared in 2000 that it referred to the attempted assassination of Pope John Paul II on May 13, 1981. John Paul II later donated one of the bullets that struck him to the Sanctuary of Our Lady of Fatima.

On May 13, 2000, John Paul II beatified the Marto siblings, or declared them “blessed,” on the 83rd anniversary of their first apparition. Their cousin, Lucia, was beatified in 2008, three years after her death at age 97. At the time, Pope Benedict XVI announced that he would waive a stipulation under ecclesiastical law that requires prospective saints to have been deceased for five years before a case for beatification can be made.

Before the Marto siblings were granted sainthood on Saturday, the church required a second miracle to be attributed to them, as is customary for prospective saints who are not martyrs. The miracle in question was approved in 2013 after a Venezuelan boy fell from a window, received a severe brain injury, but ultimately made a full recovery. The boy’s parents, Joao Baptista and Lucila Yurie, shared their story at the Fatima shrine on Thursday. According to Baptista, both he and his wife prayed to the late shepherd children for their son’s recovery. “We feel immense joy to know that this was the miracle that led to this canonization, but mostly we feel blessed by the friendship of these two children that helped our boy and now help our family,” Baptista said on Thursday.

With their canonization, the Marto siblings enter an elite group of deceased Catholic figures. A 2014 report from the Pew Research Center found that only 30 percent of popes have been canonized throughout Catholic history, with just seven being canonized in the last 1,000 years. Although canonization was once the result of popular demand, it is now rare in the Catholic Church. In addition to the pope’s approval, today’s canonization process requires an investigation on behalf of church authorities into the life, writings, and legacy of a prospective saint. Prior to the Marto siblings, the most recent canonization took place on October 16, 2016, with seven deceased figures achieving sainthood at a mass at St. Peter’s Square in Rome.