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A model of refined simplicity on the outside, the iron lady that symbolises Paris is a complicated piece of work inside her elegant A-line figure.
Custom-fitted pumps, heaters and long-life bulbs keep the 119-year-old Eiffel Tower working and sparkling, while industrial-sized cogs, gears and cables spin, bump, grind and purr deep inside the structure's innards, in places no tourists see.
Caring for the monument's hidden core is a daunting, sometimes dangerous task that goes on out of sight but keeps the tower looking its picture-postcard best. More than 500 people - from welders and plumbers to security guards and cooks - work within the structure.
"It's a village here, full of life and very specific life forms," said Yves Camaret, technical director of the company that runs the tower, as he led a tour of its many no-go areas.
Cavernous basements tucked beneath the tower's legs house massive, hydraulic motors that power the two visitors' elevators. Descending the spiral staircase into the "fosse," or pit, is like stealing onto the set of Modern Times, Charlie Chaplin's 1936 vision of industrial society. Oversized cogs spin slowly, gears painted vibrant primary colours chug, and metal cables with the circumference of a dessert plate uncoil and recoil like anacondas.
A 3,700 litre tank full of water, which was once pumped in from the nearby Seine, provides the counterbalance needed to hoist the roughly 18,000 visitors per day up to the 114.91 metre second-level landing.
The motor's myriad clanking parts need frequent oiling, and workers inspect them daily. Even a short, half-hour breakdown of one elevator can double the lines of visitors.
The company that manages the tower had a net profit of $US1.82 million ($A2.77 million) in 2007. The money goes back to its shareholders which include the City of Paris.
The tower draws some 7 million visitors annually, making it one of the world's top tourist attractions and a potential target for terrorists, though so far only in fantasy, as in the 1980 movie Superman II.
"It's a symbol, therefore it's a target," said Camaret. The tower's security detail is "extensive," he said, declining to give details.
Guards also have to watch for suicides - one jumper a year on average, Camaret said. The last was a man who leaped to his death early last year, he said.
Designed by the tower's architect and namesake, Gustave Eiffel, the visitors' elevators were installed in 1899 - ten years after the tower opened. Together with the more modern elevators that go up to the 275 metre summit observation deck, they travel more than 99,774 kilometres up and down each year.
The wear and tear takes its toll. A restoration is under way to replace all the pieces of one of the aging, hydraulic motors. Exact copies of each and every original gear, wheel and screw are being cast in foundries in France and Germany, for $US28 million ($A42.68 million), said Eric Trahand, from the elevator maintenance team.
Aside from visitors, everything else goes up and down on a modern electric elevator.
From knickknacks on sale in the gift shop to baguettes and bubbly served in the restaurants - celebrated French chef Alain Ducasse's chic Jules Verne and the casual Altitude 95 - everything goes through X-ray machines. They are then packed into sealed containers, like padlocked refrigerators on wheels, for the trip into the sky.
Subterranean pumps send water shooting up to tower-top sinks and toilets.
Dozens of miles of plumbing are integrated into the structure of the monument, exposing the pipes to the elements. Mini-heater coils prevent them freezing when the thermometer drops, so the sinks run and toilets flush even in the harshest winters.
It takes a team of 30 painters working full-time over 18 months to spruce up the tower with a fresh coat of its signature bronze paint.
Even changing a light bulb becomes a major production.
To replace one the 360 spotlights, specially trained technicians don mountain-climbing gear to scale the iron crossbeams. Working in pairs for safety, they are fastened by nylon climbers' cords to the structure at all times, with their tools strapped to their belts to prevent accidents.
"If you drop something, anything, even a thing as small as a screwdriver can kill," said electrician Henri Pellier, 44, who has worked at the Tower for 14 years.
Neither Pellier, nor his partner, 32-year-old Eric Auzolles, had any climbing experience before they were hired. They were trained by experienced mountain climbers.
"For me, climbing is a pleasure," said Auzolles as he strapped himself into a yellow harness and donned a hardhat. "It's like being on top of a mountain... We're missing out on the snow and the sun, that's all."
It can sometimes take the pair up to an hour to replace a single spotlight. Luckily, the 20,000 mini-flashbulbs that make the tower sparkle every hour on the hour throughout the night are guaranteed to last 10 years.
The centrepiece of the 1889 World's Fair, the tower represented an architectural revolution. Not only was it the world's tallest building - a title it held until the 1929 inauguration of New York's Chrysler Building - but it also marked a radical departure from Paris' hallmark low, stone buildings.
Its construction in the heart of the French capital, on the elegant Champ de Mars lawn, sparked a whirlwind of controversy. Celebrated artists, writers, architects and other prominent Parisians railed against the tower, calling in an 1887 open letter for a stop to the planned construction of the "useless and monstrous" structure.
The tower was originally meant to be demolished after twenty years, but it slowly gained public favour - and proved useful as a communications tower - thus escaping the wrecking ball.