The Eiffel Tower was built to be torn down after 20 years — a radio antenna saved it

Constructed for the 1889 World's Fair under a 20-year permit, the Eiffel Tower was slated for demolition once that permit expired in 1909. Gustave Eiffel had installed an antenna on top for early wireless telegraphy experiments, and by 1909 the tower had proven so useful for military radio communication that Paris let it stand.

— Jill Jonnes, Eiffel's Tower: And the World's Fair Where Buffalo Bill Beguiled Paris, the Artists Quarreled, and Thomas Edison Became a Count — Viking, 2009
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