Vatican Museums via EPA

Experts claim that Michelangelo's famous frescoes in the Sistine Chapel are under threat from hordes of tourists.

VATICAN CITY -- A "drunken herd" of "unruly" tourists is damaging Michelangelo’s famous Sistine Chapel paintings, one of Italy's leading arts figures claimed as the pope prepared to mark the 500th anniversary of the iconic frescoes’ creation.

Some 5 million people visit the chapel every year – sometimes as many as 20,000 in a single day -- and an increasing number of experts are now arguing that mass tourism is damaging the paintings.

Despite a major, 14-year-long restoration project in the 1990s, they claim that the breath, sweat, dust and pollution brought in by visitors dramatically changes the Chapel’s humidity and temperature – factors to which frescoes are particularly sensitive.

On Wednesday night, Pope Benedict XVI will recite the vespers in the Sistine Chapel, just as his predecessor Julius II did 500 years ago to the day.

Julius commissioned the paintings and, along with 17 cardinals, first admired the completed works, such as the Last Judgment and the Creation of Adam, as they celebrated vespers on Oct. 31, 1512.

'Unimaginable disaster'
In an article recently published by the Italian daily Corriere della Sera (in Italian), Pietro Citati, one of Italy’s leading arts and literary critics, called the conditions in the chapel an "unimaginable disaster."

He described the "unruly" tourists as a "drunken herd" who take forbidden pictures and speak loudly despite the guards’ reprimands. 

"The church needs money for its various activities," Citati wrote, "but these monstrous conditions are unacceptable."

Marco Nocca, a professor at the Art Academy in Rome, agreed.

"I understand that 5 million paying visitors per year is good business for the Vatican, but something needs to be done to limit the damage," he said.

"If they can’t restrict the number of people who visit the chapel, then maybe they should time the visits so that there are only a limited number of people in the chapel at any given time," Nocca added.

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NBC News visited the chapel one early October morning, before the gates opened to the public.

Emptied of the usual hordes of tourists, the chapel looked for once like it used to, before it became an unofficial art gallery: a place for religious worship.

The sore neck is worth it
The frescoes on the 12,000-square-foot ceiling, which contain some 300 figures, seemed like a massive biblical cartoon strip, and the silence was only broken by the thumps produced by our steps on the polished marble floors.

Never has a sore neck been more worth it, as we tilted our heads backwards for minutes to admire the ceiling.

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And this was small discomfort compared to the spasms, cramps and headaches Michelangelo suffered during the four years it took him to paint this most magnificent work of art, on scaffoldings and platforms he designed to literally rise to the occasion.

Aside from being the most famous chapel in the the pope's official residence, the Sistine Chapel is also the place where pontiffs are elected -- a rare occasion when the chapel closes its doors to the public to make way for hundreds of electing cardinals.

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The director of the Vatican Museums, Antonio Paolucci, told NBC News that a new air conditioning system would introduced early next year.

But forbidding tourists was not an option, he stressed.

"This is not only an art sanctuary, it is also a religious sanctuary, a symbol of the Catholic Church. We can't prevent people from visiting a holy place," Paolucci said.

Hours after Benedict recites vespers late Wednesday, thousands of tourists will return to pack the chapel, unfazed by the criticism. 

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