...f a crossing in force, an active campaign would be necessary to cover Baltimore, prevent the invasion of Pennsylvania, and clear Maryland. I therefore, on the 3d, ordered the 2d and 12th corps to Tennallytown , and the 9th corps to a point on the Seventh street road near Washington, and sent such cavalry as was available to the fords near Poolesville, to watch and impede the enemy in any attempt to cross i...