The eiffel tower was built as the "theme structure" of the Universal Exposition of 1889, which was held in Paris. The city originally signed a contract for an operating concession for 20 years, and after that (in 1909) the concession would revert back to the City of Paris. The tower thus remained after the exposition (the only building to be left standing from the exposition). Most of the city council wanted to tear it down at the end of the concession and sell it for scrap. However, the military discovered that it was a great antenna for the newly invented technology of radio, and so the tower was left in place. After a while people stopped talking about tearing it down, and so it's still there.