John Wesley on Deuteronomy 22:8

A battlement - A fence or breastwork, because the roofs of their houses were made flat, that men might walk on them. Blood - The guilt of blood, by a man's fall from the top of thy house, thro' thy neglect of this necessary provision. The Jew's say, that by the equity of this law, they are obliged, and so are we, to fence or remove every thing, whereby life may he endangered, as wells, or bridges, lest if any perish thro' our omission, their blood be required at our hand.