
Keaton and Clyde Bruckman, United Artists, 1926, from the Andrews Raid. Johnnie Gray (Keaton) is a Confederate engineer whose locomotive, The General, is stolen. He wants the engine back, and the girl on it. They used real trains on the Oregon, Pacific and Eastern. The bridge collapse was a single-take practical. It did not make its money back in 1927. The compositions are still the reason people teach it.
The camera is a train. Keaton stages the chase on real track with real engines and keeps the frame wide enough that you can check his work. The bridge collapse was one take because there was one train. Keep watching the edges of the frame. The joke usually arrives from there.
A gag as a load-bearing wall. Real trains on real track, the frame kept wide enough to check the work, a bridge that fell once because it could only fall once. It lost money in 1927, which tells you the audience wanted the pile-up back.
The problems at town scale. A real locomotive, real track, a real bridge that could only fall once. Johnnie Gray wants the engine and the girl back, in that order. It did not earn its money back. The frame is wide so you can check his work, and you can.