So how many people were there, anyway?
One crowd-safety expert estimated the number of people at the papal Mass on Sunday at no more than 142,000.
But his calculations included only the Benjamin Franklin Parkway west of Logan Square, as a photo showing the complete roadway was unavailable.
Add in the people standing in the less-crowded area stretching back to City Hall, as well as the untold thousands who did not get through security, and who knows?
City officials and the U.S. Secret Service are not making any public estimates for now, though a mysterious figure of 800,000-plus was on the lips of the chattering classes.
If there were that many people in the audience, however, they likely weren't all at the actual site of the Mass. For 800,000 people to gather safely on the Parkway, the street would have to be four times its actual length, give or take, depending on how many people crammed into its grassy border strips.
In other words, the street would have to stretch nearly four miles, from the papal stage near the Philadelphia Museum of Art across the Delaware River and into New Jersey.
That calculation assumes closure of the outer lanes, as was the case Sunday, and packing in four pedestrians per square meter. For the metric-challenged, that's four people in an area about the size of a card table.
Though city officials once anticipated weekend-long participation of up to 1.5 million, then later revised it to one million, Mayor Nutter said Monday that numbers weren't the point. The goal was for people to have a good Philadelphia experience, enjoy themselves, and stay safe, he said.
"That's the measure of success, not exactly how many people came or showed up," he said. "We'll look at information that gets compiled. We'll try to figure it out."
But of all the things on city government's plate, a crowd estimate is not the most pressing, he said.
And there is no answer forthcoming from the Secret Service.
"We don't do crowd estimates," Special Agent Robert Hoback said.
The rough estimate for the western end of Parkway was performed by G. Keith Still, a professor of crowd science at Manchester Metropolitan University in England.
He relied on an Inquirer photograph taken at 5 p.m. from the Top of the Tower restaurant on the 51st floor of 3 Logan Square.
Still estimated a density of three to four people per square meter in the portion of the roadway from Eakins Oval to just past 22d Street. From there to Logan Square, it thinned out to about one or two people per square meter, Still estimated after examining the photo.
He also added in crowds in adjacent ball fields and on the north side of the Franklin Institute, where densities appeared to be in the range of three to four people per square meter.
After adding up all those areas, equivalent to about 11 acres, Still came up with a total attendance in the range of 80,000 to 142,000 for the western end of the Parkway.
If inflated numbers are circulating, that is no surprise, he said, citing his experience with other mass gatherings, such as the 2011 British royal wedding.
Media outlets said a half-million people gathered on London's Mall as the royal procession passed by. At most, it was 100,000, Still said.
"What the press say, what the promoters say, and what the police say usually give you three different numbers," he said.
Yet accurate projections are important, as planners must marshal the right amount of personnel for crowd safety, he said.
"You've got to plan for the worst and hope for the best," Still said.
Inquirer staff writer Julia Terruso contributed to this article.