The opening paragraph of this powerful short story describes the scene from an objective viewpoint, as a man is on a bridge about to be hung by a group of soldiers. It is important to be aware of the perspective of this section of the story, as the narrator takes something like a camera view of the scene, not choosing yet to intrude into the consciousness of the protagonist, Peyton Farquhar. Note how the other soldiers are described as being positioned:
A sentinel at each end of the bridge stood with his rifle in the position known as "support," that is to say, vertical in front of the left shoulder, the hammer resting on the forearm thrown straight across the chest--a formal and unnatural position, enforcing an erect carriage of the body. It did not appear to be the duty of these two men to know what was occurring at the center of the bridge; they merely blockaded the two ends of the foot planking that traversed it.
What is placed at the end of either side of the bridge therefore are two soldiers, one at either end, whose job it is to be "support," which, from the description provided, is clearly more about formal procedure and strict military code in the case of such events rather than anything else, as the posture they have to adopt is obviously affected and unnatural, and they seem to play little part in the actual hanging itself. Rather they "merely blockaded" the bridge and did not seem to know what was happening at its centre.