The Vatican is continuing its preparations for Sunday's outdoor Inauguration Mass and the installation of new Pontiff – Benedict XVI, which will be the one of the last massive gatherings in St. Peter's Square, focusing on the former Cardinal Joseph Ratzinger.

Huge crowds are expected including heads of state and more than 500,000 faithful participants. Thousands of stackable chairs stretch from the steps of St. Peter's Basilica down the huge, elliptical plaza. Pilgrims are expected to arrive on Saturday night, until a few hours before the Mass starts.

"Rome is preparing for another extraordinary challenge," Mayor Walter Veltroni said. "The success of the plans implemented in the past weeks, in even more difficult conditions than the current ones, encourages us."

During the ceremony, the streets around St. Peter's will be closed to traffic, but the city was not expected to be locked down completely. Ciampino Airport, used for civilian as well as military flights and low-cost airlines will be shut down from Saturday midday until Sunday afternoon. Leonardo Da Vinci Airport should not be affected.

At the request of Italian authorities, an anti-missile system will be ready to defend the skies, along with fighter jets, helicopters and an AWACS surveillance plane deployed by NATO. Air space within a five-mile radius will be closed from 8am till 4pm.

For the service, cloudy weather is expected with a chance of light rain and winds. Receiving the pallium, a white woollen stole that will symbolise his pastoral authority and a unique papal fisherman's ring will be one of the most important moments of Pope Benedict's Inaugural Mass.

A blessing in Latin that includes "Blessed be God, who has chosen you as shepherd of the universal church, entrusting you with his apostolic ministry," will be recited by Estevez. A liturgy will end with a blessing by the new Pope, which is in Latin "Urbi et Orbi" – "To the City and to the World."