 Slough Fort was probably one of the smallest of these.The position of Slough Fort (which took its name from the now-disappeared farmsteads of Upper and Lower Slough, just west of the fort) was dictated by its position on a ridge overlooking a slope leading down to the riverside.It was the only point along a fourteen-mile stretch of the river between Cliffe to the west and Grain to the east where a landing could be effected, due to the marshes along the rest of the shoreline.