ROME (AP) -- You're expecting hundreds of thousands of guests. You don't know where they're coming from, or when they'll arrive. You don't even know the date of the celebration.
And heaven only knows the name of the man being feted.
Planning for the moment when the next pope is proclaimed to the world, and for the installation ceremony a few days later, is a big-time guessing game. And that adds up to an ungodly logistical headache for the city of Rome.
When white smoke pours out of the chimney atop the Sistine Chapel, throngs of Romans will drop what they're doing and race to St. Peter's Square to cheer the new pope when he steps out onto the balcony of St. Peter's Basilica. If the next pontiff hails from somewhere in Italy, thousands can be expected to pack trains to the capital.
Then there are all the foreigners flying into town to capture the historic moment -- an influx that may become overwhelming if cardinals break with tradition and elect the first pope from Latin America, home to 40 percent of the world's Catholics.
A tented field hospital will go up in a square near the Vatican by the eve of the start of the conclave on Tuesday, ensuring that emergency medical treatment will be just around the corner if any pilgrim feels ill or stumbles in the rush to glimpse the new pope.
While there are no other special plans for the conclave itself, Rome authorities have a detailed game-plan for the papal installation that takes place a few days after the pope is elected. The audience for that momentous event in St. Peter's Square will include presidents, prime ministers, religious leaders and tens of thousands of pilgrims, along with the throngs of accidental tourists who happen to be in town.
Police helicopters will whirl overhead. Thousands of extra police will be summoned to duty to keep streets safe and unclogged. Officers on motorized rubber dinghies will glide down the Tiber, ready to dive into the river's murky waters to pick out anything suspicious. Bomb-sniffing dogs will poke their noses down manholes and trash bins in security sweeps along the routes that both VIPs and faithful will cover en route to the square.
As soon as the installation date is known, some 500 Civil Protection volunteers, many of them ready to hop on Segways, will receive phone calls to spring into action. They know the drill for the big day: They'll report to Rome's main train station and the subway stop closest to the Vatican before dawn, helping like good shepherds to channel the flock along designated streets, closed to traffic, that lead to St. Peter's Square.
"Not even the Vatican knows how big the crowd will be," said Mario Vallorosi, who heads the Rome office of the government's Civil Protection service. "It will be affected by who (the pope) is. If he's a Latin American, he will draw huge crowds." Conservative crowd estimates, he told The Associated Press, run between 200,000 and 300,000.
Since Benedict XVI gave two-week's notice last month for his resignation -- the first in 600 years -- there have been a few "trial runs" of crowd control and security in St. Peter's Square. His final public audience drew so many people (some 150,000 people) there wasn't enough space for all in the vast cobblestone square. Surrounding streets quickly filled up with the overflow, with many faithful watching the pope's final public Vatican appearance on maxi-screens set up for them.
The Vatican's own security force, known as the gendarmerie, is in charge of the crowd inside the square and Italian police handle crowd control just outside the Vatican's boundaries. Security officers from both forces included plainclothes agents dressed up as pilgrims and tourists, listening to the chatter in the square and watching for any unusual movements.
Nearly everything went smoothly for Benedict's last public appearances, although some faithful panicked during the retired pope's penultimate Sunday blessing from his studio window, when thousands of last-minute arrivals tried to squeeze through three narrow openings through a metal fence ringing the edge of the square.
Rome enjoyed at least a few days scramble time for those last papal events. Now, uncertainty surrounding the conclave is adding huge pressure.
"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."