Looking at the picture the cylinders and heads seem to be bolted to the block in 2 cylinder units.
I am having a hard time imagining what this big of a machine was made for, but by the picture dated 1918 I suspect it was for dragging artillery around. I also suspect this is a captured piece of equipment.
Lanz was a German company, does anybody recognize the uniforms or weapons the soldiers have? The soldier on the right has his shoulder patch and rifle.