March 31, 1889: the Eiffel Tower is completed in Paris

The Eiffel Tower, 125 years old today, is one of the world’s most recognizable landmarks — and one of its top tourist destinations. In 2010, the total number of visitors topped 250 million, making it the most frequently visited paid attraction on earth.

The tower wasn’t always so popular. Paris's pointy wrought-iron structure may look charmingly old-fashioned to us now, but back when it was built in 1889, its “modern” design stirred up controversy. French artists and architects banded together to protest what they called a “useless and monstrous” tower that would dwarf existing monuments like Notre Dame cathedral and the Arc de Triomphe.

Gustave Eiffel’s construction company built the tower to commemorate the French Revolution’s centennial during the 1889 Paris World’s Fair, known as the Exposition Universelle. At about 1,000 feet tall, the tower also celebrated advances in engineering, especially in the use of metal as both a structural and decorative material.

Work entailed many detailed drawings and calculations to ensure that its 18,038 individual parts would fit together precisely. It took 300 workers two years — using cranes, wooden scaffolds, and concrete — to build the tower. The elevator inside was an even bigger problem, eventually solved with a complex system of hydraulic lifts (electric models were added later).

In the video below: Find out surprising secrets behind the Eiffel Tower's construction.

On March 31, the monument hoisted the French flag for the first time, and a 21-gun salute announced its completion….well, its near completion: the elevator wouldn’t be finished until two months later, after the French Exposition was well under way. Gustave Eiffel took a group of politicians and reporters all the way to the top via the tower's 1,710 stairs.

The Eiffel Tower surpassed the Washington Monument as the world’s tallest man-made structure, a title it would keep until New York City’s Chrysler Building was finished in 1930. The public immediately fell in love with it, eagerly lining up to pay 5 francs to go to the top. Although the original plan was to take the tower down after 20 years (which would give Eiffel time to recoup his expenses through admission fees), it was so popular by then that dismantling it was out of the question.

While some detractors eventually came around when they saw the finished tower, others didn’t: The writer Guy de Maupassant is said to have eaten his lunch in the tower every day because it was the only place in the city where he wasn’t forced to look at it.

Now, a visit to the top costs 15 Euros; many people buy their tickets online and use the mobile app to explore the tower’s history and features. Ambitious visitors (or those who need to burn off some croissant calories) climb the 600 stairs between the ground and the second observation deck. The highest observation point, 906 feet high, is only accessible by elevator.