In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.

During the American Civil War , the river , with few convenient fords and fewer bridges , provided a barrier and defensive line .
During the American Civil War , the river , with few convenient fords and fewer bridges , provided a barrier and defensive line behind which movements of troops could be accomplished with little fear of attack from the river-side flank .