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It happened to Montreal in 1976, when the Games nearly bankrupted the city and left it with a spectacularly awful Olympic Stadium that was too late, too big and too fragile. "Swifter, higher, stronger" may be a fine sporting motto, but the best legacies are those that fit. That's why, when the 2012 Games are done, London's 80,000 seater will be chopped down to 25,000.