3 millions d'années d'aventure humaine

": le CNRS et la préhistoire" was an exhibition shown at the Muséum national d'histoire naturelle between 25 January and 31 May 1979. The Fourth Doctor and Romana II walked pass a poster for it while in Paris. (TV: City of Death)

Behind the scenes
The exhibition exists in the real world at the very least in the form of a book with a matching title and a cover identical to the poster. The poster would appear to be a genuine advertisement put up at the time of filming, as location filming in Paris for the serial took place between 30 April and 3 May — a time when the poster would reasonably be up.