Prussian infantry in the time of Frederick the Great on parade in Potsdam. A clip from the East German 1962 film "Minna von Barnhelm".
Eagle-eyed readers will note that I have had this clip on this blog already but I thought it might be worth having a look at the step the soldiers are marching in - is it a reasonable approximation of the 'lock step'? I think it's a modern version but I still think it comes close.
Incidentally there's news of a forthcoming book on the armies of the Seven Years War on my Flintlock and Tomahawk blog.