In a ceremony attended by thousands of pilgrims, the 78-year-old pope carried a wooden cross at the first of the 14 'stations', which for Christians mark Christ's last journey to his crucifixion.
Wearing a red cape and flanked by a giant flaming cross, Benedict said they could not remain "neutral" when faced with the evils of the world in a five-minute address.
He drew attention to the "suffering of abused and abandoned children", the threat against the tradition family the divisions in the world and the gap between rich and poor.
The cross was carried in turn around the ancient Roman amphitheatre by young Catholics and priests and nuns from around the world before it was passed to the pope for the final station.
These included an Italian family, an American seminarist, two Franciscan monks from the Holy Land, and young people from Nigeria, Angola, Korea and Mexico, in an effort to reflect the universality of the Church.
Benedict's predecessor John Paul II took part in the Way of the Cross ceremony every year except his last, when illness forced him to follow the proceedings on television. He could barely speak when he greeted pilgrims massed in Saint Peter's Square on Easter Sunday, and died the following week.
Christians around the world also commemorated the crucifixion of Jesus Christ on Good Friday, from believers following in their saviour’s footsteps in Jerusalem to a fearful crucifying ritual in the Philippines.
The most solemn day of the Christian calendar drew thousands of pilgrims faithful to Jerusalem's Old City to join a procession along the Via Dolorosa -- the street of sorrows -- the same path Christians believe Jesus took to his crucifixion under Roman rule.
Under glorious blue skies and a brilliant sun, the crowd packed shoulder-to-shoulder carried a cross through the winding street in the heart of the Old City.
But for other Christians, Good Friday rituals were too hard to face.
A British man fled from an annual bizarre tourist attraction in the Philippines where people are crucified in bloody imitation of Jesus’ death.
Dominic Diamond joined seven Filipinos in trooping up a hill carrying huge wooden crosses in the town of San Fernando. But when it came for him to be nailed -- for a few minutes -- to the cross, he could only fall to his knees and pray, before leaving the scene in an ambulance.
There were jeers from the almost 10,000 spectators of the macabre ritual, which was originally a form of penance by devotees wanting to thank God for answered prayers or to seek help.
The leading "Kristo", Ruben Enaje, later said Diamond apologised in tears.
"He grew scared when he saw the others being crucified," Enaje said.
All seven "Kristos" were able to walk away unaided after their rituals although one needed medical attention afterwards.
Unlike their fellow faithful in the Philippines, for most Catholics the Good Friday ritual is the symbolic Stations of the Cross.
Christians in other European cities took part in Good Friday processions -- from the streets of Seville in southern Spain to Britain, where hundreds marched in the rain through the centre of London following a Jesus figure dressed in sandals and a long white tunic carrying a cross.
The solemn days of the Christians' holy week lead up to Easter on Sunday, a joyous feast day celebrating the resurrection of Jesus Christ.
While Roman Catholics and other Western Christian churches mark Easter this weekend, the Eastern Orthodox churches follow a different calendar and will celebrate Easter a week later, on April 23.