Paris's world-famous skyline has a new shape. Rising up in the midst of the Eiffel Tower, Montmartre and Montparnasse is a white monster where the giant dome of the Pantheon is usually seen.

About 20 years since the spectacular wrapping of Berlin’s Reichtag by the artist couple Christo and Jeanne-Claude, a young Frenchman has wrapped the upper section of France’s most important historical building. JR, as the 31-year-old artist calls himself, has installed a collage of thousands of black-and-white portrait photographs of important…