This picture is meant to depict the battle of Arnhem. It is a
simple  darkroom trick resulting from a shot of soldiers at
Arnhem, copied from a book - beware of copyright - and a real
picture of the bridge taken by the author.

Printing  exposure  was calculated for each  negative and a
rough sketch made on a piece of scrap paper by projecting the
images onto it, in turn, under the enlarger. A piece of card
was cut to shape as a mask between the two parts of the 
picture.

The  bridge  was exposed onto the final paper with  the mask
card shielding the top part of the paper and kept gently moving
to get a soft edge.
     
The soldiers were then printed using card to shield the already
printed image at the bottom. With skill, and some luck,
the images blend together.