Grant reached Savannah, on the east bank of the Tennessee River, about the middle of March, and in a few days began massing troops at Pittsburg Landing, six miles farther south, on the west bank of the Tennessee; still keeping his headquarters at Savannah, to await the arrival of Buell and his army. During the next two weeks he reported several times that the enemy was concentrating at Corinth, Mississippi, an important railroad crossing twenty miles from Pittsburg Landing, the estimate of their number varying from forty to eighty thousand. All this time his mind was so filled with an eager intention to begin a march upon Corinth, and a confidence that he could win a victory by a prompt attack, that he neglected the essential precaution of providing against an attack by the enemy, which at the same time was occupying the thoughts of the Confederate commander General Johnston. General Grant was therefore greatly surprised on the morning of April 6, when he proceeded from Savannah to Pittsburg Landing, to learn the cause of a fierce cannonade. He found that the Confederate army, forty thousand strong, was making an unexpected and determined attack in force on the Union camp, whose five divisions numbered a total of about thirty-three thousand. The Union generals had made no provision against such an attack. No intrenchments had been thrown up, no plan or understanding arranged. A few preliminary picket skirmishes had, indeed, put the Union front on the alert, but the commanders of brigades and regiments were not prepared for the impetuous rush with which the three successive Confederate lines began the main battle. On their part, the enemy did not realize their hope of effecting a complete surprise, and the nature of the ground was so characterized by a network of local roads, alternating patches of woods and open fields, miry hollows and abrupt ravines, that the lines of conflict were quickly broken into short, disjointed movements that admitted of little or no combined or systematic direction. The effort of the Union officers was necessarily limited to a continuous resistance to the advance of the enemy, from whatever direction it came; that of the Confederate leaders to the general purpose of forcing the Union lines away from Pittsburg Landing so that they might destroy the Federal transports and thus cut off all means of retreat. In this effort, although during the whole of Sunday, April 6, the Union front had been forced back a mile and a half, the enemy had not entirely succeeded. About sunset, General Beauregard, who, by the death of General Johnston during the afternoon, succeeded to the Confederate command, gave orders to suspend the attack, in the firm expectation however, that he would be able to complete his victory the next morning.