Why did Jim and his mother wait in a dich

The pirates were routing their house. Jim and his mother managed to escape.

This was certainly the end for both of us, I thought. How I cursed the cowardice of the neighbours; how I blamed my poor mother for her honesty and her greed, for her past foolhardiness and present weakness! We were just at the little bridge, by good fortune; and I helped her, tottering as she was, to the edge of the bank, where, sure enough, she gave a sigh and fell on my shoulder. I do not know how I found the strength to do it at all, and I am afraid it was roughly done, but I managed to drag her down the bank and a little way under the arch. Farther I could not move her, for the bridge was too low to let me do more than crawl below it. So there we had to stay—my mother almost entirely exposed and both of us within earshot of the inn.