Retired Pope Benedict XVI is expected to attend the canonization of Blesseds John XXIII and John Paul II on Sunday, said Msgr. Liberio Andreatta, head of the Vatican-related pilgrim agency, Opera Romana Pellegrinaggi.
"Never before have there been two popes canonized and two popes living," he said at a news conference Wednesday in Rome to discuss final plans and preparations for pilgrims. "You can imagine their emotions."
However, Jesuit Fr. Federico Lombardi, Vatican spokesman, continued to caution journalists, saying that while the retired pope certainly had been invited to the Mass, "we'll have to wait and see" if, at 87 years old, he feels up to attending.
During the canonization Mass, Andreatta said, priests will be stationed amid the crowds in St. Peter's Square and along the broad Via della Conciliazione, leading to the square, in order to distribute Communion even to those far from the altar.
Planning for the predicted arrival of millions of visitors has been a daunting task for both the Vatican and the city of Rome.
"Still, we want to make this event livable," Andreatta stressed. "We also had to meet expenses, which we have done thanks to sponsorship."
Of the 40-some sponsors, the largest single contributor was ENI, the multinational energy agency which is Italy's largest single industrial company, he said.
Maurizio Pucci, director of special events planning for the city of Rome, told reporters that while the city has been informed officially of the arrival of 58 chartered planes and 700 buses coming from all over Europe, the actual number of visitors cannot be calculated.
"Many more are expected," Pucci said. "Our concerns have included arranging parking spaces for this unknown number of buses." The parking must be close to public transportation so the passengers can reach the center of Rome.
For buses arriving from abroad, overhead signs on major highways have been programmed to provide directions in English, Polish, French, as well as Italian, he said.
Street cleaners are already working overtime, Pucci added, and their chores include keeping the 980 portable toilets clean and odor-free.
Security is a prime concern. From 7 p.m. Saturday, the evening before the canonization, most of central Rome will be off limits to vehicles, except police cars, ambulances and cars carrying visiting heads of state. Tight security measures will extend to the Tiber River banks and Rome's underground tunnels and catacombs. However, access to St. Peter's Square and to Via della Conciliazione will be open to everyone on foot, Andreatta said.
In its preparations, the Rome diocese is reaching out to the digital generation through tweets and a free app available in English, Spanish and Polish, as well as Italian.
The app -- Santo Subito -- provides such pragmatic details as maps, the time and place of events, the addresses of the churches which will remain open for a prayer vigil Saturday night, and spiritual reflections based upon the teachings of both future saints. The app, developed with the help of volunteer university students, is available for both Android and IOS formats.
The Rome diocesan office promoting Blessed John Paul's cause also has a YouTube page  with videos in a variety of languages.
Andreatta said in addition to the 17 large video screens that will be erected around the center of Rome for pilgrims wanting to avoid the bigger crowds, another will be set up in Terminal 3 of Rome's Leonardo da Vinci International Airport and one in the square in front of the cathedral of Milan in northern Italy.