What was the narrator doing at the bridge? Why?

The narrator of the story, the author Hemingway himself, was there to explore the bridgehead and find out to what point the enemy forces had advanced. 
 
Earnest Hemingway was a war correspondent covering the Spanish Civil War. So he was there to collect the news about the progress of the Nationalist forces towards Ebro.

In the story Old Man at the Bridge the scene is created before us that the old man Was forced to leave his town because of the enemy attack.

He travelled 12 Km and now he was not able to walk any further. He was resting on the side of a bridge as he was very tired. Moreover he was sitting there even knowing about the danger to sit there because he was pondering upon only his animals that he had left behind. The thought made him very sad and he was just sitting still at the bridge and was worried about the animals.