Tens of thousands of faithful were gathering Sunday near St Peter's Square ahead of a mass in which Pope Benedict XVI was to beatify his predecessor, the late John Paul II, dpa reported.
Metal detectors at entrances leading to the square were activated and police helicopters hovered overhead amid tight security measures. Dozens of international leaders were expected to attend the ceremony.
In the Catholic Church, beatification marks the penultimate stage in the process to make someone a saint, something which many of the faithful have clamoured for since John Paul's death on April 2, 2005.
Officials estimated that some 1 million people were to attend the beatification, which began with a night vigil Saturday at the Circus Maximus, once an ancient Roman chariot-racing arena.
After Sunday's mass, the faithful were to be allowed to file past a casket containing John Paul's remains, on display inside St Peter's Basilica.