PARIS — One cloudy afternoon this month, the line to enter the Louvre stretched around the entrance pyramid, across one long courtyard and into the next. Inside the museum, a crowd more than a dozen deep faced the Mona Lisa, most taking cellphone pictures and selfies. Near the Winged Victory of Samothrace, Jean-Michel Borda, visiting from Madrid, paused amid the crush. "It's like the Metro early in the morning," he said.
It is the height of summer, and millions of visitors are flocking to the Louvre — the busiest art museum in the world, with 9.3 million visitors last year — and to other great museums across Europe. Every year the numbers grow as new middle classes emerge, especially in Asia and Eastern Europe. Last summer the British Museum had record attendance, and for 2013 as a whole it had 6.7 million visitors, making it the world's second-most-visited art museum, according to the Art Newspaper. Attendance at the Uffizi in Florence for the first half of the year is up almost 5 percent over last year.
Soaring attendance has turned many museums into crowded, saunalike spaces, forcing institutions to debate how to balance accessibility with art preservation.
In recent years, museums have started doing more to manage the crowds. Most offer timed tickets. Others are extending their hours. To protect the art, some are installing new air-conditioning systems. Still, some critics say that they're not doing enough.
Last year, the Vatican Museums had a record 5.5 million visitors. This year, thanks to the popularity of Pope Francis, officials expect that to rise to 6 million. The Vatican is installing a new climate-control system in the Sistine Chapel to help spare Michelangelo's frescoes the humidity generated by the 2,000 people who fill the space at any given time, recently as many as 22,000 a day. The Vatican hopes to have it finished by October.
Museums generally don't like keeping a lid on attendance. At the Hermitage, which had 3.1 million visitors last year, the only cap on the number of visitors is "the physical limitations of the space itself, or the number of hangers in the coat room during the winter," said Nina V. Silanteva, the head of the museum's visitor services department.
Silanteva said the goal was to make the museum in St. Petersburg, Russia, accessible to as many people as possible, but she conceded that the crowds pose problems. "Such a colossal number of simultaneous viewers isn't good for the art, and it can be uncomfortable and overwhelming for those who come to see the art," she said. "Thankfully nothing bad has happened, and God has saved us from any mishaps."
Sometimes, mishaps do occur. Because of crowds, the Townley Venus in the British Museum, a first- to second-century Roman statue with an outstretched arm, has had its fingers knocked off a few times in recent years.
Even when the art is secure, the experience can become irksome. Patricia Rucidlo, a guide in Florence for Context Travel, said that visiting the Accademia, famous for Michelangelo's David, had become "a nightmare" this year because visitors are now allowed to take photos. "People now swarm the paintings, step on anyone to get to them, push, shove, snap a photo, and move quickly on without looking at the painting," she wrote in an email.
Lines outside the Uffizi in Florence, which had 1.9 million visitors last year, are famed for their length, and the courtyard is filled with people scalping timed tickets. (A private company handles ticketing at the Uffizi and keeps 14 percent of the ticket price.) The museum says that it caps the number of visitors at 980 people at a time, to meet fire codes.
But earlier this year, some staff members warned that the museum had been letting in far more people than allowed, putting the artwork at risk. Tomaso Montanari, an art historian in Florence and professor at the Federico II University in Naples, has been strongly critical of crowding at the Uffizi, which is considerably smaller than other major museums. "It seems like a tropical greenhouse — you can't breathe," he said in a telephone interview.
Marco Ferri, a spokesman for the Uffizi, said the museum has been under renovation since 2006 but that some rooms have not yet been upgraded with climate control. "In the next two years, everything will be modernized," he said.
The Louvre, Uffizi, Vatican, Rijksmuseum in Amsterdam and Prado in Madrid all offer timed tickets for sale, allowing visitors to avoid lines. Even museums that don't charge admission to their permanent collections, like the British Museum and the National Gallery in London, have special exhibitions that require paying tickets. During the National Gallery's Leonardo da Vinci blockbuster in 2011, websites were reselling $25 tickets for as much as $400.
While most museums are closed at least one day a week, in 2012 the Prado, in Madrid, moved to a seven-day-a-week schedule and extended its hours until 8 p.m. on weekdays. That followed a redesign in 2007 that improved the circulation at the museum.
At every museum, people do find ways to circumvent the lines, going to the Louvre on Wednesday and Friday evenings when the museum is open until 9:45 p.m., finding less-trafficked entrances or even paying for an annual membership that allows priority access.
Standing in a long line next to I. M. Pei's entrance pyramid, Manu Srivastan, 46, of Jabalpur, India, said he had come with his wife, father and daughters. They had been waiting for about 45 minutes, with 15 more to go, but they didn't mind. "It's a wonderful learning experience," he said of the Louvre. "You're always left wanting more."