Under a splendid Roman sun, the German pope presided at a colorful celebration where tens of thousands of people waved palm and olive branches to commemorate Jesus' entry into Jerusalem the week before he was crucified.
The pope, who turned 84 on Saturday, wove his sermon around the theme of man's relationship with God and how it can sometimes be threatened by technology.
"From the beginning men and women have been filled -- and this is as true today as ever -- with a desire to 'be like God', to attain the heights of God by their own powers," he said, wearing resplendent red and gold vestments.
"Mankind has managed to accomplish so many things: we can fly! We can see, hear and speak to one another from the farthest ends of the earth. And yet the force of gravity which draws us down is powerful," he said.
While the great advances of technology have improved life for man, the pope said, they have also increased possibilities for evil, and recent natural disasters were a reminder, if any were needed, that mankind is not all-powerful.
If man wanted a relationship with God he had to first "abandon the pride of wanting to become God," said the pope, celebrating his sixth Easter season as the leader of the world's some 1.2 billion Roman Catholics.
After the mass, the pope appealed for peace in Colombia, calling for wide participation in a day of prayer for the victims of violence to be held there on Friday. "Enough of violence in Colombia. May she live in peace," he said.
START OF HOLY WEEK
Palm Sunday, a moveable feast that is marked on the Sunday before Easter, is celebrated throughout the Christian world to commemorate Jesus' entry into Jerusalem on a donkey, a symbol of peace in the ancient world.
At the ceremony a cantor recounted all the events in Jesus' life between Palm Sunday and Easter. Via Della Conciliazione, the broad boulevard leading to the Vatican, was bedecked with olive trees and bronze statues depicting the "stations of the cross," or the last events in Jesus' life.
For the pope and Christians around the world, it marks the start of a hectic week of events leading to Easter Sunday.
On Holy Thursday, Benedict will preside at two traditional services in the Vatican, including one in which he will wash and kiss the feet of twelve men in a gesture of humility toward his apostles the night before he died.
On Good Friday he will preside at services in the Vatican and then lead a traditional torch-lit Via Crucis, or Way of the Cross, around the ruins of Rome's ancient Colosseum.
Holy Week services at the Vatican culminate on Easter Sunday, the most important day in the liturgical calendar, when the pope delivers his twice-yearly "Urbi et Orbi" (to the city and the world) blessing and message.