"The biggest concern is lack of information," said Giammario Nardi, the man Rome's mayor has put in charge of hosting special events.
Nardi insisted the city is not privy to any hints from the Vatican about when the papal installation will take place. "We're operating on predictions," he said, "on what the newspapers tell us."
Nardi spoke with The Associated Press several hours before the Vatican announced on Friday that the cardinals will start voting for Benedict's successor on Tuesday, a process that could wrap up in a day or two, or might need more time.
With a shudder, Nardi recalled how ambulances were blocked by the narrow streets of the Borgo, the neighborhood near the Vatican, when faithful couldn't squeeze into the square and clogged the streets after John Paul II's death in 2005. In those days crowds turned out day and night to pray at the Vatican and pass by his body as it lay on display in St. Peter's Basilica.
The decision to set up a field hospital this time is fruit of that bad memory, he said.
The most mentioned date for the new pope's installation Mass in St. Peter's Square is Sunday, March 17, exactly a week before Palm Sunday begins Holy Week. Nardi acknowledged that date as the city's operating "hypothesis."
He sighed as he pondered the challenges.
"The election of an Italian pope or a foreign pope will mean, as pilgrims go, different numbers and different types," he said, adding: "It's not like we have a lot of time between when the white smoke puffs out and the installation."
Complicating a March 17 papal installation: It's the same date the capital is hosting the Rome Marathon.
Some 100,000 runners are expected for the race, which traditionally loops near St. Peter's Square in mid-morning. That's practically the same time huge crowds could be surging toward the Vatican for a first papal Mass.
Nardi said that the Italian government wanted to cancel the marathon, citing worries about public safety. But Rome's officials were adamant about holding it, and a compromise was clinched.
If the installation falls on marathon day, the race will go ahead but re-routed away from the Vatican. The marathon's start will also be put off until early afternoon, when presumably the new pope, pilgrims and Romans will be eating lunch. A main Rome boulevard usually on the marathon route will be fenced off so limousines can whisk VIPs straight to St. Peter's Square without dodging pedestrians — or marathon runners.
If the marathon weren't enough, March 17 is also St. Patrick's Day, with thousands of Irish rugby fans expected in Rome because Ireland plays Italy the day before in the Six Nations tournament.
Benedict's final public audience cost Rome some euros 500,000 ($675,000) alone, and public events surrounding the new pope's installation ceremony could cost 10 times that amount.
For example, the city will rent several maxi-screens, at euros 20,000 ($27,000) apiece, to place in streets near the Vatican for faithful who can't fit into the square.
Rome Mayor Gianni Alemanno has taken to passing a collection plate to the central government, but so far Italy's austerity-minded caretaker premier, Mario Monti, hasn't dropped anything in.
Whether Rome could recoup some of the costs connected with the papal ceremonies from tourism, including a modest surcharge on hotel rooms, depends heavily on where the pilgrims come from, Nardi said. The number of tourists in the city rose by some 10 to 20 percent for Benedict's final audience, with many apparently from southern Germany, judging by the many pilgrims waving the flag of Benedict's native Bavaria.
When Benedict was installed in 2005, an estimated 100,000 Germans turned out for the ceremony, which drew some 350,000 overall.
Just how many people the new pope will attract to the city is an open question, depending a lot on what Nardi called "charisma."
Fulvio Paolocci contributed reporting.