VATICAN CITY -- Francis, the first Jesuit and the first Latin American to become pope, called for protecting the environment, the poor and the weak as he was officially installed Tuesday in an inaugural Mass in St. Peter's Square.
The inauguration drew world leaders, princes, religious figures and a throng of 200,000 people, many of them enthralled by the new pope's emphasis on simplicity, humility and social justice. Francis became the 266th pope and spiritual leader of the world's 1.2 billion Roman Catholics.
Speaking to a crowd waving national flags from around the world, Francis, 76, continued the focus on the disadvantaged that he has shown since his surprise election to the papacy a week ago. He is the first pope to select the name of St. Francis of Assisi, who was known for his charity, work with the poor and devotion to nature.
"Let us never forget that authentic power is service and that the pope too, when exercising power, must enter ever more fully into that service which has its radiant culmination on the cross," Francis said in his homily.
"He must be inspired by the lowly, concrete and faithful service which marked St. Joseph and, like him, he must open his arms to protect all of God's people and embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important, those whom Matthew lists in the final judgment on love: the hungry, the thirsty, the stranger, the naked, the sick and those in prison."
Listening to him were 132 VIPs from around the world, sitting close to an altar set up in front of St. Peter's Basilica. Among them were Argentina President Cristina Fernandez de Kirchner, Italian President Giorgio Napolitano, German Chancellor Angela Merkel, Prince Albert of Monaco, Vice President Joseph Biden and Rep. Nancy Pelosi (D-Calif.).
The pope made a strong call to political leaders to protect the environment and not let the "omens of destruction and death accompany the advancement of the world."
"Please, I would like to ask all those who have positions of responsibility in economic, political and social life, and all men and women of goodwill: Let us be 'protectors' of creation, protectors of God's plan inscribed in nature, protectors of one another and of the environment," he said.
Religious leaders from Christian, Muslim and Sikh organizations also took front-row seats, reflecting Francis' emphasis on interfaith understanding. They included Bartholomew I, the spiritual leader of the world's Orthodox Christians. It was the first time in nearly 1,000 years that a leader of the Istanbul-based church has attended a papal inauguration.
Displaying the penchant he has shown in the past week for bucking tradition and tossing aside security worries so he can get close to the public, before the Mass began Pope Francis zigzagged around barricaded aisles inside St. Peter's Square in a white, open jeep. He waved to the cheering crowds, stopped to kiss a baby and embraced a disabled man.
In contrast, his predecessors Benedict XVI and Pope John Paul II often used a "pope mobile" enclosed in bulletproof glass. The reason was in 1981 Pope John Paul II, riding in an open car in St. Peter's Square, was shot and critically wounded.
Many in the crowd Tuesday cheered wildly, shouted out the pope's name and swarmed toward his vehicle, pressing up against barricades.
"It's something we're never going to experience again in our lives," said Alesia Santacroce, 24, of Caracas, Venezuela, who was touring Italy and awoke at 5 a.m. to rush over to St. Peter's Square to see the pope's installation.
Elvis Godoy, 27, a seminarian also from Venezuela who is studying in Rome, said in Spanish that Pope Francis "has captivated the world with his personality, his humility and his closeness with the people."
"It's a source of pride to have a pope from Latin America," Godoy added, a Venezuelan flag draped around his shoulders.
Tuesday's ceremony began at 9:30 a.m. inside St. Peter's Basilica. In a gesture to Christians in the East, the pope prayed with Eastern Rite Catholic patriarchs and archbishops in front of the tomb of St. Peter before leading the procession of cardinals and clergyman into the square.
During the ceremony, Pope Francis received a fisherman's ring traditionally given to new popes. Unlike those of previous popes, his was made of silver, not gold, at his request. He also received the pallium, or papal scarf, that represents his new role as spiritual leader of Catholics worldwide.
The multilingual event was celebrated in both the European languages native to the church, such as Italian and Latin, as well as Spanish and Chinese, the languages of the growing number of Catholics worldwide.
From the beginning of his pontificate, Francis has surprised the faithful and media alike with humble gestures, raising hopes among his followers that he might live up to his name. But those who have reported on him for years say that though his approach might break with Vatican tradition, it is nothing new.
"It's not a fabrication and there's no marketing expert behind him, telling him what to say," said Pope Francis' authorized biographer, Sergio Rubin of Argentina. "He's always been this way, and wants to continue being this way, simple and austere."
In his first days as pope, Francis passed up the papal Mercedes-Benz for a modest sedan. He also turned down the pair of red loafers his predecessor Benedict XVI was always seen wearing. Instead, he sported his own worn-down pair of black shoes. One day, he even stepped out of his role as pope to pay a pending hotel bill
Tuesday in St. Peter's Square, Paola Gheddo, 42, said she traveled from her home in northern Italy partly because her son, Francesco, 6, said he wanted to see the pope who shares his name.
"He's very happy to have the same name as the pope," Gheddo said. "We are here because we love this pope."
With Angelica Marin