Pope Francis was greeted by crowds of hundreds of thousands as he made saints of two shepherd children at the Fatima shrine complex in Portugal.
"We declare the blissful Francisco Marto and Jacinta Marto saints," the pontiff said to loud applause.
It is 100 years since the two - and a third child - reported seeing the Virgin Mary while tending sheep. The third is also on the way to sainthood.
Portugal boosted security and re-imposed border controls temporarily.
Some 500,000 worshippers gathered in the town of Fatima, north of Lisbon, for the ceremony on Saturday, the Vatican said in a statement.
Roman Catholic pilgrims converged on the Fatima Sanctuary from countries as far away as China, Venezuela and East Timor.
The town's local bishop first read out the request for the two "little shepherds" to be canonised before the Pope declared them both saints of the Catholic Church.
Earlier on Saturday, the official Twitter account of the Pope posted a message with reference to the Virgin Mary.
"Whenever we look to Mary, we come to believe once again in the revolutionary nature of love and tenderness," it said.
The pontiff also met Portuguese Prime Minister Antonio Costa for a private meeting ahead of the ceremony.
Plea for harmony
On Friday, Pope Francis flew into Fatima in a helicopter and travelled through the town in his "Popemobile".
At a candle-lit vigil he called for harmony between all people at the Chapel of the Apparitions and spoke of wars "tearing our world apart".
The chapel is built on the very spot where the Virgin Mary is said to have appeared.
Two of the children - Jacinta and Francisco Marto - have been canonised for the miracles attributed to them. They died in the 1918-1919 European influenza pandemic.
The so-called three secrets of Fatima were written down by their cousin, Lucia dos Santos, who died in 2005 aged 97. The beatification process for her began in 2008.
The Church attaches great value to their visions, as Mary is believed to have revealed truths to help mankind. The Church says the first vision came on 13 May 1917.
In a video message to the people of Portugal, the Pope said he was going to present himself to Mary "and I need to feel you close, physically and spiritually, so that we are one heart and one mind".
What are the three secrets?
They are prophecies written down by Lucia, years after the apparitions that the three said they had witnessed. She spent her adult life as a nun at a convent in Coimbra.
The first two secrets in Lucia's account were revealed in 1942.
- The first described a terrifying vision of hell, with a "great sea of fire", demons and human souls
- The second is interpreted as Mary's prediction that World War One would end and that World War Two would start during the papacy of Pius XI
- Mary also called for the "consecration" of Russia, saying: "If my requests are heeded, Russia will be converted, and there will be peace; if not, she will spread her errors throughout the world, causing wars and persecutions of the Church"
- Lucia sealed the third secret in an envelope, which was handed to the Vatican in 1957 and only revealed in 2000
- It described an angel demanding "penance!", then the Pope and other clergy climbing a mountain, only to be killed by soldiers firing bullets and arrows.
What does the Vatican say about them?
According to Pope Francis's predecessor, Benedict XVI, the visions described in the three secrets are "meant to mobilise the forces of change in the right direction".
They are not like the Bible - a text he describes as a "public revelation".
The Fatima visions are "private revelations", he writes. Their purpose is "to help live more fully" in accordance with Christ's teaching.
The late Pope John Paul II was shot by a Turkish gunman on 13 May 1981.
He believed that his survival was due to Mary's divine intervention, and that the third secret had predicted the attack on him.
John Paul donated the bullet to Fatima, and it was inserted into the crown adorning a statue of Mary there.
What about Pope Francis's visit?
He follows John Paul II and Benedict XVI, who also made pilgrimages to the Fatima Sanctuary.
Security was high at the site, with Portugal deploying 6,000 police and emergency workers. Concrete blocks were placed on approach roads, to stop any terrorist "ramming" attack with a vehicle.
Only nine border crossings remained open, with systematic checks, as Portugal temporarily suspended the Schengen open borders pact.
Local accommodation over the weekend was far more expensive than usual, as hotels and residents cashed in on the papal visit.