Pope Francis led a Palm Sunday service the day after he was discharged from hospital following a bout of bronchitis, and urged the world to take better care of the poor, the lonely and the infirm.
Thousands of people waved palm and olive branches as Francis was driven into St. Peter's Square sitting in the back of a white, open-topped vehicle, before descending and starting the service from beneath an ancient Egyptian obelisk.
The pope, 86, was taken to Rome's Gemelli hospital on Wednesday after complaining of breathing difficulties, but recovered quickly following an infusion of antibiotics and returned to his Vatican residence on Saturday.
Looking to allay concerns about his health, the Vatican has said he will take part a full array of Easter events this week, the busiest period in the Roman Catholic Church calendar, starting with the open-air Palm Sunday service.
The pontiff, wearing red vestments, spoke with a quiet, but clear voice as he addressed a crowd of more than 30,000 faithful in weak spring sunshine. In his homily he called on people not to ignore those experiencing great suffering and solitude.
"Today their numbers are legion. Entire peoples are exploited and abandoned; the poor live on our streets and we look the other way; migrants are no longer faces but numbers, prisoners are disowned; people written off as problems," he said.
The pope, who marked the 10th anniversary of his pontificate in March, has long highlighted the plight of the poor and of migrants.
He has suffered a number of ailments in recent years, including severe knee pain, which means he uses a cane and often a wheelchair in his public appearances.
His difficulties with mobility have limited his participation at some events, and as happened last year, a senior cardinal celebrated the actual Mass on Sunday.
Palm Sunday marks the day that the Bible says Jesus rode into Jerusalem to the cheers of the crowds, the week before Christian believe he rose from the dead following his execution on the Cross.
On Holy Thursday, Francis will celebrate Mass in a prison for juveniles in Rome. It is not yet clear if he will participate in the traditional Good Friday Via Crucis (Way of the Cross) procession around Rome's ancient Colosseum.
The pope, head of the world's nearly 1.4 billion Roman Catholics, will then preside over the Mass on Easter Sunday, the most important day on the Christian liturgical calendar, where he is expected to read his "Urbi et Orbi" (to the city and the world) message.