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Brian, that piece of Prussian music was written in 1795.
General Field marshal Von Bloecher and his regiments were playing this tune as they appeared from the woods and marched on to Waterloo battlefield, just as Napoleon was preparing to send his regiments over in the final attack one hour before dusk, as he had done so many times and won.
The saying went, that if you hadn't defeated Napoleon by 4 o'clock, he would cross over the field with massed regiments and win. The Brits had 5 rounds left per man at that hour, and when the unknown regiments made their appearance from the wooded landscape, many thought it was the 30,000 French soldiers that had been sent out to pursue the Prussians two days earlier after a previous battle which Napoleon had won as the sun was setting.
The Brits believed they were surrounded and prepared to make a last stand, determined to fall with rifle and bayonet in one last counter onslaught.
But then they heard the march music, they realised the Prussians had come, that they had led Napoleon's other 30,000 soldiers astray and lost them in the fog and woods somewhere.
The roar of the cheers coming from the red-coated Brits was so great, it is said it was heard as far as Brussels, the Ardennes and Westminster in London.