France decided to make a fake city of Paris to keep German planes from bombarding the real city. The fake city was built just north of the real one. There were electric lights, replica buildings, and even a copy of the Gare du Nord—the station from which high-speed trains now travel to and from London.
The plan would have worked because the radars were much more primitive in 1918. The war ended before they could finish the fake city, so it was never put to test. The only remains we have today are pictures taken back then.