Leo emerged in St. Peter`s Square in his popemobile at the end of an evening Mass that kicked off the Jubilee of Youth, a weeklong celebration for young Catholics. The estimated 120,000 young pilgrims who had packed the square erupted in shocked cheers and chants, as Leo looped around the square and up and down the boulevard leading to it

For 20 minutes, Leo beamed, waved and clearly seemed to enjoy the outpouring of enthusiasm from his perch on the popemobile, as he took in the sea of cheering, flag-waving young people from around the world as the setting sun cast a golden glow over the basilica

In a brief off-the-cuff salute and blessing from the altar, he told the young pilgrims that they were beacons of light, hope and peace that the world needs today

"The world needs messages of hope. You are this message, and must give hope to everyone," he said in a mix of Spanish, English and Italian. "We want peace in the world. We want peace in the world!"

Leo, the first American pope, hadn`t been expected to meet with the young pilgrims as a group until the weekend, when he was to preside over a vigil Saturday and Mass on Sunday in the highlight of the Jubilee week

Tuesday`s Mass had been celebrated by the Italian archbishop who organized the Holy Year, Archbishop Rino Fisichella, but it was he who urged the kids to not leave the square at the end, because the pope "had a surprise for us"

The crowd responded with the classic refrain from Catholic youth gatherings: "This is the youth of the pope"

This week, downtown Rome has swarmed with energetic, singing and dancing masses of teenage Catholic scouts, church and Catholic school groups whose numbers are expected to swell to 500,000 by the weekend

It all had the vibe of a scaled-down World Youth Day, the once-every-three-year Catholic Woodstock festival that was inaugurated by St. John Paul II and maintained by every pope since