During September's great papal convergence, when well over a million Catholics and associated others are expected to blanket the city from river to river, more than a few visitors might want to see the riches arts and culture groups have worked hard to lay out before them.

Right there on the Parkway, at the locus of festivities for Pope Francis' visit, an exhibition of Bibles beckons at the Free Library. The Franklin Institute is flying in treasures from the Vatican. And for a knowing crowd, a postcard-sized 15th-century oil by Jan van Eyck at the Philadelphia Museum of Art awaits the devotional gaze, its title of suddenly modern relevance: Saint Francis of Assisi Receiving the Stigmata.

But the ability to take in the city's cultural riches will be hindered. Citing the long hand of the U.S. Secret Service and the Department of Homeland Security as well as logistical hurdles, several - if not all - of the arts groups along the Parkway are expecting to be compelled to close for the two or three peak days of festivities, Sept. 25-27.

Arts leaders say they are thrilled for the visibility the event will bring - and distressed to be letting all those visitors and dollars slip through their fingers.

"There is a little bit of frustration and disappointment, but it is unfair to use those terms without saying that we understand that safety is paramount," said Troy Collins, the Franklin Institute's senior vice president of earned revenue, marketing, and operations. "We live in a very scary world, and we want everyone to be safe."

The Parkway will be the site of the Saturday Festival of Families for the World Meeting of Families, the gathering that is attracting Francis to Philadelphia. As many as 1.5 million people are expected to throng to the festivities that will feature the Philadelphia Orchestra, the Italian tenor Andrea Bocelli, and Colombian superstar Juanes.

The next day, the pope will celebrate Mass on the Parkway and again, throngs of as many as 1.5 million are expected.

"We would love to be able to be open, but the museum will most definitely be closed Saturday and Sunday," said Philadelphia Museum of Art president Gail Harrity, who is still holding out the hope that Friday hours can be preserved.

Plans are not final for every arts group, but during the last weekend in September, in addition to the Art Museum, the Barnes Foundation will close at least Saturday and Sunday. The Free Library of Philadelphia's Parkway, Independence, and Rittenhouse branches, as well as Library for the Blind and Physically Handicapped, will close Saturday and Sunday.

The Franklin Institute expects to shut down its Giant Heart and quiet its Big Brain for the weekend, but is still hoping to keep open the part of the building housing "Vatican Splendors," which opens Sept. 19. For now, ticket sales to the show are on hold.

"We want the Secret Service and Homeland Security to read our plan and bless it," says Collins. "We'd rather lose a few advance sales and not disappoint anyone," he said.

The closure of arts and culture groups may extend well beyond the Parkway. Museums around Independence Mall, also bracing for the crush of humanity, will hold a meeting Wednesday to discuss who might close and for how long. The Kimmel Center does not yet know whether its building will be open that weekend. The Rosenbach of the Free Library of Philadelphia is assembling a show called "Catholics in the New World," but will be closed Saturday and Sunday.

The Vatican announced last week that Pope Francis would make an appearance on Independence Mall on Saturday, discussing immigration and religious freedom. That is expected to bring as many as 50,000 people into the historic area, organizers said.

Arts groups that had hoped for a revenue bonanza are still waiting to know the full financial fallout. While ticket sales will be lost, some groups will be able to recoup revenue by renting out facilities for private events related to the World Meeting of Families and papal visit. On the other hand, the deluge also means added bills for security and other operating expenses.

Whether or not they will stay open to the public, some groups are anticipating that staff will not be able to get to work, and are considering keeping workers overnight for several days - and everything that would entail.

"We might bring in food, temporary bedding, facilities for showers, having meals prepared right there - it'll be a movie night for staff," says Collins. "It's a challenge, but it's still a historic moment for the city."

Leaders of the Academy of Natural Sciences believe it's more likely than not that they will be closed for a stretch. But the animals must still be fed, requiring humans to take up residence alongside the reptiles. "It's a disappointment to have to close down when you are the oldest natural history museum in the Western Hemisphere," said Sara Hertz, vice president of strategic initiatives.

"A day of lost revenue means probably $15,000 to $25,000 for us," says Margaret "Peg" Zminda, CFO and COO of the Barnes, which will be closed. "So two weekend days of lost revenue is not insignificant, but we are trying to develop some strategies to recover that." In addition to potential rentals, the Barnes may extend hours on the weekdays leading up to the weekend it will close.

Arts groups are considering an expense-reward equation to staying open for a crowd that, spiritual though it may be, will also have more immediate earthly concerns. Big events on the Parkway tend to bring a greater number of people looking for bathrooms than Medieval manuscripts or Dada and Surrealist photographs, several said.

Which is just one more reason that arts groups are concerned about the proliferation of large events on the Parkway.

"It's a once-in-a-generation event, and the museum is thrilled to support the city," says Harrity of the papal visit. That said, she continued, these big events - the several dozen concerts, races, parades, and other events now happening on the Parkway - draw big crowds that do not generally patronize museums, while, at the same time, they scare off regular visitors concerned about traffic, parking, and crowds.

"As the city increases the number of events, they also need to be thoughtful about addressing the impact of lost revenues for all of our institutions, and consider how to best address it," she said.

The Barnes, for instance, decided to close on Independence Days because of huge crowds on the Parkway who came for entertainment and fireworks - but not the museum. "You would see results that would be a lot less than a normal day, and it wasn't financially advantageous," Zminda said.

As for the papal convergence, Harrity said she did not know whether it would mean a net loss for the Art Museum, since rentals are not finalized. "A lot of plans are very much in flux," she said.

Meryl Levitz, president and CEO of Visit Philadelphia, says it's hard to measure the residual effects for arts and culture groups from having the spotlight on the city. She says Philadelphia will host 8,000 members of the media alone as the media center for not just the area but also New York and Washington.

"That's one audience that can be very directly addressed about Philadelphia's presence in the arts and culture world and how much things have changed," she said. "If everyone who is going to be in Philadelphia has a wonderful time and tells friends and family that it wasn't the easiest time but is worth a return visit, that payoff is down the line as well."

Said Levitz: "It's inconvenient sometimes to be a part of history."