Ok, first, this is a wonderful action movie. Not exactly Michael Bay in scale, but faaaaaar better in story and visual intensity. The difference between these two is that most of what Bay does is eye-candy with little depth, and this would be more like a gourmet meal. Burt Lancaster is obviously not French, and does not try to be, but his acting along with his fellow cast members is spot on. They have an intensity born out of having lived through a war and a lean-ness of spirit that reflects too many years of soul-crushing occupation.
It's the end of WWII in Europe and Nazis are fleeing France ahead of the Allies arrival, but being Nazi's, they decide to steal a fortune in valuable art by putting it on one of the last trains leaving for Germany. Not wanting their heritage to be stolen, the French Underground turns to Burt Lancaster, a French railroad station yard manager and leader of an ever-shrinking resistance cell. They just need to delay the train a few day until the allies arrive.
Movies like this are a time-stamp for history. What was important then, may well have become insignificant to us now. Most people born in this century have no idea what WWII was about much less why this movie would be important. But remember something. You had family living back then. Family that saw this as history, not fiction. When you watch, see how things looked, watch how people lived. Your great-great grandparents lived in this world.
Oh, and as you watch, remember that this was done nearly 60 years ago and it still holds up as a gripping story, even by today's standards.