3 P.M.
Though both of these attacks were successful , the resistance of the Confederates had in each case been sufficient to gain time for Jackson . On the 15th Harper 's Ferry surrendered , and McClellan continued to advance ; Longstreet prepared for battle . The next day , at nightfall , the Federals were facing Lee 's army , the Antietam creek flowing between the hostile ranks . At 3 P.M. of the 17th , A.P. Hill 's division , after a forced march of seventeen miles , and after fording the Potomac , found itself in front of the left wing of the Federal army , -- consisting of Burnside 's corps , -- which had already brushed away the opposition in its front , and was now advancing to seize the ford at Shepherdstown and cut off Lee from the Potomac . A.P. Hill rode into battle at the head of his division . The few brigades which , had been opposed to Burnside had offered a stout resistance , but , too weak to resist long , had fallen back to our right . Into the gap we were ordered .