Rome - Some 10 000 police have been deployed in Rome to boost security ahead of Friday's Via Crucis, or Way of the Cross, procession at the Colosseum.
Pope Francis was due to preside over the centuries-old ceremony, a re-enactment of the 14 stops that Catholics believe Jesus made on Good Friday as he was led to his crucifixion.
"Look upon Christ Crucified: our hope for eternal life is born in Him," Francis tweeted before the night-time procession at one of the world's most famous landmarks.
Italian police were on high alert for the event, following a spate of anti-terrorism arrests this week and reports that the Islamic State terrorist group has singled out Rome as a target.
The city is seen by Islamists as the centre of "an enemy religion," Italian anti-Mafia and anti-terrorism chief prosecutor Federico Cafiero de Raho told RAI state radio on Thursday.
A no-go area for heavy goods vehicles was set up around central Rome and the Vatican, and police intervened Friday to stop a Turkish truck whose driver was reportedly unaware of the security measures.
Before the procession, usually watched by thousands of people, Francis was to lead a Passion of the Christ service in St Peter's Basilica.
This week is marked by several ceremonies for the Catholic Church leading up to Easter, celebrating the resurrection of Jesus.
On Saturday, Francis is to lead an Easter vigil Mass in St Peter's Basilica, and celebrations culminate Sunday with Easter Mass and the "Urbi et Orbi" (To The City and To The World) message and blessings.