VATICAN CITY (AP) -- Pope Francis has walked solemnly through St. Peter's Square in a Palm Sunday procession to usher in Holy Week ahead of Easter.

Pope Francis celebrates a Palm Sunday Mass in St. Peter's Square at the Vatican . (AP Photo/Andrew Medichini)

Francis clutched a palm frond for the religious service, celebrated outside St. Peter's Basilica. In keeping with the simple tone of his two-year-old papacy, Francis leaned on a plain wooden pastoral staff instead of a traditionally more ornate one as he stood under a red canopy on the basilica steps.

Francis and other prelates at the Mass wore bright red vestments to recall Jesus' death by crucifixion. Tens of thousands of faithful held olive branches during Mass under a brilliantly blue sky.

Tourists and pilgrims have poured into Rome, and many will follow the pope's Way of the Cross service at the Colosseum Friday.

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