Grant's army at that time numbered about 43,000 men, and he decided to make a campaign into the interior of Mississippi while waiting for General Banks from Baton Rouge to join him. The Confederate army under Pemberton numbered about 40,000, and about 15,000 more Confederates were at Jackson, Miss., under command of General Joseph E. Johnston. It was against Johnston's army that Grant decided to move. Johnston, on being attacked by Grant, fell back from Jackson and took a position on Champion's Hill, where a hard battle was fought in which the Confederates were greatly outnumbered and gave way in confusion. Part of Pemberton's army had arrived and was engaged in this battle. Pemberton retreated towards Vicksburg, closely followed by Grant, and several short engagements between the two armies took place on the road to Vicksburg. The Federal army now invested the city, occupying the surrounding hills. Around the doomed city gleamed the thousands of bayonets of the Union army. The city was filled with soldiers and the citizens of the country who had fled there for refuge and were now penned in. On May 22d Grant ordered a grand assault by his whole army. The troops, flushed with their victories of the last few days, were eager for the attack. It is said that his columns were made up with his taller soldiers in front and the second in stature in the next line, and so on down, so as to save exposure to the fire of the enemy. At the appointed time the order was passed down the line to move forward, and the columns leaped from their hiding places and started on their disastrous march in the face of a murderous fire from the defenders of the city, only to be mowed down by the sweeping fire from the Confederate batteries. Others came, crawling over the bodies of their fallen comrades, but at every charge they were met by the missiles of death. Thus it continued hour after hour until the coming of darkness. The assault had failed and the Union forces retired within their entrenchments before the city. This is considered as one of the most brave and disastrous assaults of the war. The army now settled down to the wearisome siege, and for six weeks they encircled the city with trenches, approaching nearer and nearer to the defending walls. One by one the defending batteries were silenced. On the afternoon of June 25th a redoubt of the Confederate works was blown up with a mine. When the same exploded the Federals began to dash into the opening, only to meet with a withering fire from an interior parapet which the Confederates had constructed in the anticipation of this event. Grant was constantly receiving reënforcements, and before the end of the siege his army numbered 70,000. Day and night the roar of artillery continued without ceasing. Shrieking shells from Porter's fleet rose in grand curves, either bursting in midair or on the streets of the city, spreading havoc in all directions.