Vatican City ? Pope Benedict XVI blessed palm fronds and olive branches Sunday in the Vatican, opening a ritual-filled Holy Week that pilgrims in Jerusalem celebrated in a procession retracing Jesus’ triumphant return to the holy city some 2,000 years ago.

Wearing embroidered red vestments, Benedict processed through St. Peter’s Square in Rome, which was lush with the palms and olive trees that are emblematic of the ceremony.

The pope told tens of thousands of people gathered under a brilliant springtime sun that the olive branches were symbols of Christ’s peace, the palms symbols of his martyrdom. Palm Sunday marks the beginning of the church’s weeklong commemoration of the last days of Christ’s life and his resurrection on Easter Sunday in the Christian tradition.

“With this liturgical assembly we enter into Holy Week, to live the Passion, death and resurrection of Jesus Christ,” Benedict said in an opening prayer of the Palm Sunday Mass.

Pope John Paul II had made a tradition of dedicating Palm Sunday to the world’s young people, and Benedict continued that legacy in his first year as pope.

After the Mass, young people from Cologne, Germany, which hosted last year’s World Youth Day, formally handed over the large wooden cross used during the church’s international celebration to a group of youngsters from Sydney, Australia, who are hosting the next gathering in 2008.

Dressed in traditional Bavarian highland attire, a German boy and his father carry their bouquets of decorated catkins in Ramsau, southern Germany. They were taking the bouquets to church for consecration, following an old tradition on Palm Sunday.

Benedict told them that for many, the cross on which Christ was crucified signified only his death and sacrifice. “But Palm Sunday tells us that … it is the cross that is the true tree of life,” he said, calling the cross a symbol of poverty, peace and the universality of the church.

According to tradition, Jesus rode into Jerusalem on a donkey a week before his crucifixion as followers spread palm branches in his path.

On Sunday in Jerusalem, some 20,000 pilgrims from around the world joyously waved palm fronds and flags as they marched from the Mount of Olives into the holy city.

The Latin Patriarch of Jerusalem, Michel Sabbah – the top Roman Catholic official in the Holy Land – led the procession, which included a mix of young and old, as local Scouts in assorted uniforms walked alongside elderly nuns and priests in colorful robes.

The march drew large crowds for the second year in a row, after several years when pilgrims stayed away because of Israeli-Palestinian violence. Armed Israeli police on horseback and on motorcycles accompanied the procession.

A cacophony of sounds filled the air as some marchers strummed guitars and others banged drums and hoisted loudspeakers – playing songs and prayers in a variety of languages. Others hummed nearly silent hymns.

“It reminds me of a Thanksgiving Day parade,” said Sister Catherine Hurley from Newton, N.J. “It’s not how I would do it, but I’m happy that they are doing it.”

Nevertheless, Hurley, a Salesian sister with a large cross hanging from her neck, said she was “overwhelmed” by the number of Christians “of all shapes and sizes” converging in the Holy Land.