ALONG the old Roman road that crosses the rolling hills from the upper waters of the Marne to the Meuse, a soldier of France was passing in the night. In the broader pools of summer moonlight he showed as a hale and husky fellow of about thirty years, with dark hair and eyes and a handsome, downcast face. His uniform was faded and dusty; not a trace of the horizon-blue was left; only a gray shadow. He had no knapsack on his back, no gun on his shoulder.