The Eiffel Tower has never been mentioned in dialog, but it has appeared numerous times in establishing shots of Paris. In fact, the script of "Homefront" is the only Star Trek script to mention the Eiffel Tower in its stage directions. It was built in 1889, and has since become the symbol of France. It was designed by the Human Gustav Eiffel, who also designed the structural framework for the Statue of Liberty in New York City; coincidentally, the scene in ENT: "Storm Front, Part II" in which Hitler views the statue from a boat in New York Harbor was created by digitally altering footage taken at the Eiffel Tower when he visited conquered Paris in 1940.
The non-canon novel Trapped in Time mentions that the Eiffel Tower was destroyed during the Third World War and later rebuilt. The front cover of the novel depicts the Eiffel Tower during the Nazi occupation in spite of the fact that all of its 1944 scenes take place in Normandy.